ON THE

RELATIONS, STRUCTURE, AND FUNCTION, OF THE VALVES

OF THE

VASCULAR SYSTEM IN VERTEBRATA.

BY

JAMES BELL PETTI GREW, M.D., Edin.,

ASSISTANT IN THE MUSEUM OF THE ROYAL COLLEGE OF SURGEONS OF ENGLAND ; EXTRAORDINARY MEMBER
AND LATE PRESIDENT OF THE ROYAL MEDICAL SOCIETY OF EDINBURGH ; LATE RESIDENT
SURGEON TO THE CLINICAL SURGICAL WARDS OF THE ROYAL INFIRMARY
OF EDINBURGH, ETC., ETC.

REPRINTED FROM THE

TRANSACTIONS OF THE ROYAL SOCIETY OF EDINBURGH, Vol. XXIII. Part III.

EDINBURGH:

PEINTED FOR THE SOCIETY BY NEILL AND COMPANY.

MDCCCLXIV.

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C 761 )

XLVI. — On the Relations, Structure, and Function, of the Valves of the Vascular
System in Vertebrata. By James Bell Pettigrew, M.D. Edin., Assistant
in the Museum of the Royal College of Surgeons of England. Communicated
by William Turner, M.B. (Plates XXVIII., XXIX.)

(Read 521st March 1864.)

Introductory Remarks. ,

The rapid advances made of late in the diagnosis of cardiac and other diseases
affecting the organs of circulation, render the present inquiry into the normal or
healthy condition of the valves of the vascular system, not more important
anatomically, than medically. As the nature and composition of the parts in
which valves are found in some instances materially influence their action, I
have deemed it necessary to advert briefly to the properties and structure of the
veins and arteries, when describing the venous and arterial or semilunar valves ;
and to the arrangement of the muscular fibres in the ventricles, when point-
ing out the peculiarities of the auriculo-ventricular ones. As, moreover, much
information is to be obtained by comparing analogous structures, I have, in
the present instance, not confined my observations to any particular form
of valve, but have examined in succession the entire valvular arrangements
of the fish, the reptile, the bird, and the mammal ; my object being to arrive, if
possible, at a correct knowledge of the more elaborate varieties as they exist in
man, and in the higher mammalia.

In order to simplify the numerous relations and complicated structure of the
several valves met with, as well' as to obviate the necessity for entering largely
into anatomical details, the present paper has been fully illustrated by photo-
graphs and drawings from dissections, and from casts representing the valves in
action. The photographs, thirty-four in number, were taken for the most part
from the specimens while in the fresh or recent state, by Mr Ayling and myself.
Of the drawings, twenty-three in number, that marked 33, Plate XXVIII. and
the last six of Plate XXIX., are by my friend Dr Henry Season Wilson. The
remaining fourteen are by myself. For permission to examine and figure several
of the specimens illustrating the peculiarities of the valvular arrangements of the
fish and reptile, I am indebted to the kindness of the Council of the Royal College
of Surgeons of England. The dissections and casts, which are numerous, were
made with a special view to this inquiry, and are preserved in the Museum of the
Royal College of Surgeons of England, where they may be consulted.
vol. xxiit. part hi. y s

762 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

Structure of the -Veins and Venous Valves.

Regarding the composition of the veins, there is, as the reader is aware, some
difference of opinion, authorities not being agreed either as to the number or
nature of the coats. This may in part be explained by the variation in the
thickness of the coats themselves, these, according to John Hunter,* becoming-
thinner and thinner in proportion to the size of the vein, the nearer they ap-
proach to the heart. In moderate-sized veins an external, a middle, and an
internal coat are usually described ; the first consisting of cellular, fibrous, and
elastic tissue, interlacing in all directions ; the second, of waved filaments of
areolar tissue, with a certain admixture of non-striped muscular fibres, which
run circularly, obliquely, or even longitudinally ; f the third, consisting of one
or more strata of very fine elastic tissue, minutely reticulated in a longitudinal
direction, the innermost stratum (when several are present) being lined by
epithelium. Of these layers, the second and third, from the fact of their contri-
buting to the formation of the venous valves, are the most important. The coats
of the veins, as has been long known, are tough, elastic, and possessed of con-
siderable vital contractility. Of these qualities, the toughness prevents undue
dilatation of the vessel when distended with blood ; the elasticity and vital con-
tractility assisting the onward flow of that fluid, and tending to approximate the
segments of the valves, by contracting in the direction of the axis of the vessel.
As the valves of the veins are very ample and very flexible, they readily accom-
modate themselves to the varying conditions in which they are placed by the
elasticity and contractility of the vessel, and by the reflux of the blood.

The valves of the veins vary as regards the number of the segments com-
posing them, and also slightly as regards structure. In the smallest veins, and
where small veins enter larger ones (Plate XXVIII. fig. 0 b), one segment only is
present. In middle-sized veins, as they occur in the extremities, two segments
(Plate XXVIII. figs. 3, 4, and 7 ab), are usually met with;]; while in the larger
veins, as in the internal jugular of the horse, three, and even four segments (Plate
XXVIII. figs. 1 and 2, abc,fgh), are by no means uncommon.§

The segments, whatever their number, are semilunar in shape [] (Plate XXVIII.

* Hunter on the Blood, pp. 180, 181.

"I" Dr Chevers says, that in the deep as well as in some of the superficial veins of the trunk
and neck, the middle coat is composed of several layers of circular fibres, with only here and there
a few which take a longitudinal coxirse ; while the middle coat of the superficial and deep veins of
the limbs consists of a circular layer, and immediately within this of a strong layer of longitudinal
fibres. — Med. Gazette, 1845, p. 638.

J In the heart of the frog-fish, sun-fish, sturgeon, American devil-fish, python, and crocodile,
a semilunar valve, consisting of two segments, guards the orifice of communication between the
sinus venosus and the right auricle.

§ When four segments are present, two are usually more or less rudimentary (Plate XXVIII.
fig. 2/<jr).

|| John Hunter in speaking of the form of the venous valves, says, their free edges are cut off
straight, and are not curved as in the arteries. This, however, is not the case ; as may be seen by

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA.

763

figs. 3 and 4 a b) ; the convex border being attached to the wall of the vessel
obliquely (Plate XXVIII. fig. 5 a b), the crescentic or concave margin, which is
free (Plate XXVIII. fig. 4 c), and directed towards the heart, projecting into the
vessel. When one segment constitutes the valve, and it occurs in the course of
a vein, it is placed obliquely in the vessel (Plate XXVIII. fig. 9), its attached
convex border (a) occupying rather more than a half of the interior. When the
segment occurs at the junction of a smaller with a larger vein, its convex border
is attached to a half or more of the orifice of the smaller one where it joins the
larger, its free margin running transversely to the larger trunk. In such cases
the segment acts as a moveable partition or septum, common alike to both vessels,
but its position and relations are such, that while it readily permits the blood
from the smaller vein to enter the larger one, it effectually prevents its
return.

When the valve consists of two segments, they are semilunar in shape, and
very ample, the vertical measurement of each, being not unfrequently nearly
twice that of the diameter of the vessel itself (Plate XXVIII. figs. 3 and 4 a I). In
such cases both segments are usually of the same size, so that they divide the
vessel into two equal parts (e). They are placed obliquely with regard to each
other (Plate XXVIII. fig. 5 a b), their convex borders, which are attached to the
interior of the vessel, starting from a common point above (Plate XXVIII. fig. 2 i),
and gradually diverging {e) to curve round and reunite on the opposite side of the
vessel (d) ; their concave and free margins inclining towards each other (Plate
XXVIII. fig. 12 e), and being directed, as in the more simple valve, towards the
heart. The free margins of the two segments, like the attached ones, start from
a common point (Plate XXVIII. fig. 4 r), but such is the shape of the segments,
and such the angle at which they are placed with regard to each other, that they
do not diverge to the same extent, but run more or less parallel* This relation
of the segments to each other above, is in part accounted for by the presence of
a fibrous structure (Plate XXVIII. fig. 4 r), which extends from the wall of the
vessel into the interior, and supports them at a certain distance from the sides
of the vessel. The fibrous structure referred to is well seen in the semilunar
valves of the pulmonary artery and aorta (Plate XXVIII. fig. 36 n n'), and seems
to have escaped observation. In a line corresponding to the attached border of
each of the segments (Plate XXVIII. fig. 4 a b), the middle and internal coats
of the vein are thickened, as may be ascertained by a vertical section, or by

reference to photographs 1, 2, 3, and 4, Plate XXVIII. The edges referred to are least curved when
the valve is distended or in action (Plate XXVIII. fig. 13 e), but the curve is never altogether
absent.— Treatise on thi Blood, pp. 181, 182.

* I was much struck, on injecting the external saphenous vein of the human subject from the
dorsum of the foot, to find, on dissection,- that the free margins of some of the segments were in
contact throughout ; clearly showing, that when the segments are allowed to float in a fluid, they are
so projected against each other, that even the slightest reflux will instantly close them.

704 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

introducing coloured piaster of Paris* into the vessel. I particularly direct
attention to this circumstance, as the thickenings referred to form fibrous zones
i Plate XXVIII. fig 6 h\ which extend for a short distance into the substance of the
segments, and afford them a considerable degree of support. They further assist in
preserving the shape of the segments, and in enabling them to maintain the proper
angle of inclination — the said angle inclining the segments towards each other in
the mesial plane of the vessel (Plate XXVIII. figs. 3 and 4 <?). When a valve,
consisting of two segments, is situated at the junction of a smaller with a larger
vein, one of the segments is usually placed between the two vessels at the point
of juncture (Plate XXVIII. fig. 11 &),the other on the wall of the smaller vein (a).
The position of the segments in such instances varies, their long diameter some-
times running parallel with the larger vessel, sometimes obliquely, but more
commonly transversely. When the valve consists of three segments (Plate XXVIII.
figs. 1 and 8, a be, r s t), the segments, as a rule, are unequal in size, one of them
being generally a little larger (t) than either of the other two (r s). They are semi-
lunar in shape, as in the smaller and middle-sized veins, and differ from the latter
in being less capacious. The tri-semilunar valves in the veins, may therefore be
regarded as intermediate between the fully developed bi-semilunar valves found
in the veins of the extremities, and the fully developed tri-semilunar valves which
occur at the origin of the pulmonary artery and aorta. The existence of valves
in the veins is indicated externally by a dilatation or enlargement of the vessel ;
the dilatation consisting of one, two (Plate XXVIII. figs. 3, 5, and 12 h g), or three
(Plate XXVIII. fig. 8 gab) swellings, according as the valve is composed of one
two, or three segments. These dilatations or swellings are analogous to the
sinuses of Valsalva in the arteries (Plate XXVIII. figs. 17 and 18 d), their
direction in the veins of the extremities being from below upwards and from
within outwards. They form, with the segment to which they belong, open
sinuses or pouches which look towards the heart, and as they extend nearly as
far in an outward direction as the segments project inwardly, they give a very
good idea of the size and shape of the segments themselves. The only point
regarding the dilatations deserving of special attention, is the gradual thinning in
a direction from above downwards, of those portions of the coats of the vessel
which enter into their formation. The thinning referred to, is well seen when
vertical sections of the vessel are made, or when the vein is distended with
coloured plaster of Paris, as recommended. The swellings present a deeper
colour the nearer we approach to the attached border of the segments, the
attached borders, on account of their greater thickness, appearing as dense fibrous
zones (Plate XXVIII. fig. 5 a b, fig. 6 h). The object of the swellings is evidently

* I have derived much information from the employment of this material ; its use having
enabled me to determine with something like accuracy, the relation of the segments of the valves to
each other when in action, and other points connected with the physiology of the heart.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA.

7G5

twofold,— -firstly, to cause the blood to act on the segments of the valve from above
downwards, and from without inwards, in the direction of the mesial plane, or of
the axis of the vessel, according as there are two or three segments present;
and, secondly, to increase the area over which the 'pressure exerted by the reflux
of the blood extends. When the vein is opened between the segments, when two
are present, each of the segments is seen to form two curves, — one curve giving
its concave or free margin (Plate XXVIII. fig. 4 c), the other its convex or
attached one {a) ; but when the section is carried through the wall of the vein, and
through the centre of one of the segments, one curve only is obtained (Plate
XXVIII. fig. 3 g) ; and it is useful to remember this, as it shows with what facility
the structures entering into the formation of the segments, viz., the lining mem-
brane of the vessel and certain parts of the middle and internal coats, are given
off. It also shows how the lower portion of the dilatation (g), while it supports
a certain quantity of the refluent blood, guides by far the greater quantity on to
the valves (b), rendering their closure not a matter of accident, but of necessity.

The segments of the venous valves are exceedingly flexible, and so delicate as
to be semi-transparent. They possess great strength and a considerable degree
of elasticity * Usually they are described as consisting of a reduplication of the
fine membrane lining the vessel, strengthened by some included fibro-cellular
tissue, the whole being covered with epithelium. This description, however, is
much too general to convey any very accurate impression of their real structure,
and the following, drawn up from the examination of a large number of specimens
taken from man, the horse, ox, sheep, and other animals, may prove useful.

When one of the segments of a well-formed bi-semilunar valve removed from
the human femoral vein, is stained with carmine, fixed between two glasses, and
examined with the microscope or pocket lens, the subjoined phenomena are wit-
nessed : —

1st, The lining membrane of the vessel covered with epithelium is seen to
form the investing sheath of the segment, no breach of continuity being any-
where perceptible.

2d, Large quantities of white fibrous tissue, mixed up with areolar and
yellow elastic tissue, from the middle and internal coats of the vessel, are observed
to extend into the segment. The fibres composing these tissues pursue a definite
arrangement.

Thus running along the concave or free margin of the segment (Plate
XXVIII. fig. 14 a), as likewise on the body, especially where the segments join
each other (&), are a series of very delicate fibres, consisting principally of
yellow elastic tissue. These fibres proceed in the direction of the long diameter

* Hunter denies the elasticity of the segments, on the ground that the valvular membrane is
not formed of a reduplication of the lining membrane of the vessel, an opinion at variance with recent
investigation. — Treatise on the Blood, pp. 181, 182.

VOL. XXIII. PART III. 9 T

76*G DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

of the segment, but transversely to the course of the vessel, and may be denomi-
nated the horizontal fibres.

Running in a precisely opposite direction, and confining themselves principally
to the body of the segment, are a series of equally delicate fibres (c), having a like
composition, and which, for the sake of distinction, may be described as the
vertical series. These two sets of fibres are superficial, and to be seen properly,
a power magnifying from 200 to 250 diameters is required.

Radiating from the centre of the segment (Plate XXVIII. fig. 15 e) towards its
attached border (ii'), and seen through the more delicate horizontal and vertical
ones, is a series of stronger and deeper fibres, composed of white fibrous and yellow
elastic tissue, the former predominating. Still stronger and deeper than either
of the fibres yet described, and proceeding from the attached border of the
segment (Plate XXVIII. fig. 16 s t), is a series of oblique fibres, continuous in very
many instances with corresponding fibres in the middle coat of the vessel. These
fibres cross each other with great regularity, and form the principal portion of the
segments. They are most strongly marked at the margin of the convex border of
the segment, where they form a fibrous zone or ring, which, as has been explained,
supports the segment, and carries it away from the sides of the vessel into the
interior. I have also detected, in the vicinity of the attached border of the
segment, some non-striped muscular fibres. The segment of a venous valve is
therefore a highly symmetrical and complex structure, the fibrous tissues com-
posing it, being arranged in at least three well-marked directions ; viz., horizontally,
vertically, and obliquely. The great strength which such an arrangement is cal-
culated to impart to the segment is readily understood.

In conclusion, the segment is thinnest at its free margin, and thickest towards
its attached border ; the body being a little thicker than the free margins, and
where the extremities or narrow portions of the segments join each other, but
not so thick as the attached border.

The Venous Valves in Action.

The manner in which the venous valves act, is well seen when the vein is sus-
pended perpendicularly overhead, and water, oil, glycerine, or liquid plaster of
Paris, poured into it by an assistant from above ; the vein beneath the valve being
cut away, the better to expose the segments to the view of the spectator. When
the valve consists of one segment only, the fluid is observed to force it obliquely
across the vessel, and to apply its free crescentic margin to the interior or convex
surface with such accuracy as to prevent even the slightest reflux. When two
segments occur in the course of a vein, they are forced by the fluid simultaneously
towards each other in the mesial plane of the vessel (Plate XXVIII. figs. 3 and 12 <?),
the sinuses (gh) behind the segments becoming distended, and directing the

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 767

current and regulating to a certain extent the amount of pressure. The closure in
this instance is almost instantaneous, and so perfect that not a single drop
escapes. It is effected by the free margins of the segments, and a, large proportion
of the sides, coming into accurate contact, the amount of contact increasing in the
inverse of the pressure applied. If liquid plaster of Paris be used for distending
the vein, and the specimen is examined after the plaster has set, one is struck
with the great precision with Avhich the segments act (Plate XXV III. figs. 6 and
11 a h), these coming together so symmetrically, that they form by their union a
perpendicular wall or septum (Plate XXVIII. figs. 6, 11, and 12, e) of a beauti-
fully crescentic shape* (Plate XXVIII. fig. 13 e). This fact is significant, as it
clearly proves that the concave or free margins of the segments, and a consider-
able proportion of the sides, run parallel to each other when the valve is in action,
a circumstance difficult of comprehension, when it is remembered that the convex
borders of the segments are attached obliquely to the walls of the vessel, and that
the segments, when not in action, incline towards each other at a considerable
angle. The very accurate apposition of the segments, when the valve is closed, is
to be traced : —

I ] st, To the direction and shape of the venous sinuses, which conduct the fluid
employed, on to the segments in almost equal quantities.

2d, To the disposition of the free margins of the segments, which, as was
explained, run side by side, and are supported by fibrous structures which
carry them away from the sides of the vessel for some distance ; and,

3d, To the amplitude of the segments themselves, which allows them to
come together without difficulty, and when the pressure is applied, to flatten them-
selves against each other to form the perpendicular crescentic wall adverted to.

In the event of two segments occurring at the entrance of a smaller into a
larger vein, one of them being situated at the junction of the smaller vessel with the
main trunk (Plate XXVIII. fig. 11 b), the other on the wall of the tributary branch
{a) ; the former, i.e., the common or septal segment, is forced by the fluid in a
slightly outward direction, the latter in an opposite or inward direction, the free
margins and sides of the segments being by this arrangement accurately applied to
each other to form an impervious wall or septum (e) as already described. When
the entrance of a smaller into a larger vessel is guarded by two segments situated
on the tributary branch at its orifice, their action is precisely the same as when
they are placed in the course of a vein. When three segments are present, as
happens in the larger trunks, the closure is effected in a manner greatly re-
sembling that by which the semilunar valves of the pulmonary artery and aorta

* In order to see the perpendicular wall formed by the flattening of the sides of the segments
against each other when the valve is in action, the vein and the plaster should be cut across im-
mediately above the valve, and the segments forcibly separated by introducing a thin knife between
them. In fig. 13, Plate XXVIII., one of the segments has been quite removed.

768 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

are closed ; the fluid employed, in virtue of the direction given to it by the
venous sinuses, causing each of the segments (Plate XXVIII. fig. 8 r s t) to bend
or doable upon itself at an angle (i) of something like 60°;* the three lines formed
by the doubling and union of the three segments dividing the circle corresponding
to the wall of the vessel, into three nearly equal parts. In the doubling of the
segments upon themselves, each segment regulates the amount of bending which
takes place in that next to it, and as the free margins of the segments so bent
advance synchronously towards the axis of the vessel, they mutually act upon
and support each other. As the three segments are attached obliquely to the
wall of the vessel, while the free margins, after the folding has taken place, are
inclined towards and run parallel to each other {a b), they form an inverted
dome consisting of three nearly equal parts, the margins of the segments, and a
certain portion of the sides, when the pressure is applied, flattening themselves
against each other to form three crescentic partitions or septa f which run from
the axis of the vessel towards the circumference.

The tri-semilunar valve, as will be seen from the foregoing explanation, is
closed in a very different manner from the bi-semilunar one. The occlusion of
the vessel, however, is not the less complete ; the segments, when three are present,
being wedged into each other in a direction from above downwards, and from
without inwards ; the first of these movements, by tending to flatten the segments,
pressing their margins and sides together : the second, by urging the segments
towards the axis of the vessel, impacting them more and more tightly, especially
towards their apices or points. As the apices or points formed by the doubling
of the segments whilst in action, are composed principally of the flexible and free
crescentic margins, and are at liberty to move until the wedging process is com-
pleted, a careful examination has satisfied me, that they rotate to a greater or less
extent before the valve is finally closed. This spiral movement, which is simply
indicated in the venous valves, is more strongly marked in the semilunar ones of
the pulmonary artery and aorta (Plate XXVIII. figs. 26, 27, and 28, % w, and
attains, as will be shown subsequently, a maximum in the auriculo-ventricular
valves of the mammal (Plate XXIX. figs. 53 and 54, min, s r).

By whatever power the blood in the veins advances — whether impelled by the
heart alone, or by muscular contractions occurring in different parts of the body,
or by rythmic movements which take place in the vessels themselves, or by
efforts of inspiration, or by all or combinations of these ; there can, I think, be
little doubt that this fluid, in its backward or retrograde movement, acts to a
great extent mechanically on the valves as described. It ought, however, to be
borne in mind that the veins and the valves are vital structures, and that

* The angle is never precisely 60°, from the fact of the segments varying slightly as regards size,
f The crescentic partitions, as they occur in the semilunar valves of the pulmonary artery and
aorta, are shown at b b', of fig. 25, Plate XXVIII.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA.

769

although a perfect closure may be effected by purely mechanical means in the
dead vein, it is more than probable that in the living one, the contraction of the
coats of the vessel exercises a regulating influence.

Structure of the Arteries and Arterial Valves.

The coats of the arteries, as is well known, are thicker than those of the veins,
while the layers composing them are more numerous. The external coat, accord-
ing to Henle, consists of an outer layer of areolar tissue in which the fibres run
obliquely or diagonally round the vessel, and an internal stratum of elastic tissue ;
the middle coat in the largest arteries, according to Rauschel, being divisible into
upwards of forty layers. The layers of the middle coat consist of; pale, soft,
flattened fibres, with an admixture of elastic tissue, the fibres and elastic tissue
being disposed circularly round the vessel. The internal coat is composed of one
or more layers of fibres, so delicate that they constitute a transparent film, the
film being perforated at intervals, and lined with epithelium. The arteries, as
might be expected from their structure, and as was proved by the admirable ex-
periments of John Hunter, whose beautiful preparations I have had an oppor-
tunity of examining, possess a high degree of elasticity and vital contractility,
and are extensible and retractile both in their length and breadth ; the power of
recovery, according to that author, being greater in proportion as the vessel is
nearer the heart. From this it follows that the pulmonary artery and aorta are
most liable to change in dimensions. As, however, any material alteration in
the size of the pulmonary artery and aorta might interfere with the proper
function of the semilunar valves situated at their orifices, it is curious to note
that the great vessels arise from strong and comparatively unyielding fibrous
rings. These rings (particularly the aortic one) are so dense as to be almost
cartilaginous in consistence, and Professor Donders* has lately discovered, that
they contain stellate corpuscles similar in man}' respects to those stellate and
spicate corpuscles, found in many forms of cartilaginous tumours. They have
been more or less minutely described by Valsalva,! Gerdy4 Dr John Reid,§
and Mr W. S. Savory, || and merit attention because of their important relations
to the segments of the semilunar valves. The following description of the aortic
and pulmonic fibrous rings, has been drawn up chiefly from the examination of a
large number of human hearts. Each ring, as will be seen by a reference to

* " Onderzockingeu betrekkeligh den bouw van het menchclijke hart," in " Nederlandsch
Lancet" for March and April 1852.

f Opera Valsalva, torn. i. p 129.
T Journal Complimentaire, torn. x.

§ Cyc. Anat. and Phy. article " Heart," pp. 588, 589. London, 1839.
|] Paper read before the Royal Society in December 1851.

VOL. XXIII. PART III. 9 U

770 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION

Plate XXVIII. figure 30, taken from a photograph of a boiled heart, consists,
as was shown by Reid, of three convex portions (rst). Each convex portion is
directed from above downwards, and from without inwards, and as it unites
above with that next to it, the two when taken together form a conical-shaped
prominence (#), which is adapted to one of the three triangular-shaped inter-
spaces occurring between the segments of the valve (Plate XXVIII. fig. 17 h).
The arterial rings are therefore placed obliquely, the under surface, which gives
attachment to many of the fibres of the ventricles anteriorly (Plate XXVIII. fig.
30 dd'\ resting on the rounded oblique border of the ventricular walls (Plate
XXVIII. fig. 17 e). The ring surrounding the pulmonary artery, as was pointed
out by Reid, is broader, but not quite so thick as that surrounding the aorta,
and both are admirably adapted for the reception of the large vessels which,
as was shown by that author, originate in three festooned borders. These
borders, I am inclined to think, consist of two parts, — an outer (Plate XXVIII.
fig. 17 r r'), composed of the outer, and a small portion of the central layer of
either the aorta or pulmonary artery; and an inner (t), composed principally
of the central and inner layers. The outer border (Plate XXVIII. fig. 18 r),
which is the thinner of the two, is attached to the superior and outer margin
of one or other of the fibrous rings (g), chiefly by the serous membranes ; the
inner (Plate XXVIII. fig. 17 t), which projects further in a direction from
above downwards, and corresponds to the thickened convex border of the seg-
ments (s), to the formation of which it contributes, being attached to the
inferior and inner margin (g). These points are well seen, when a vertical
section is made of the aorta or pulmonary artery between the segments com-
posing the semilunar valves. In such a section (Plate XXVIII. fig. 17), the
vessels are observed to be thickened in a direction from above downwards,
the thickening beginning at the point where the segments meet above (b), and
gradually increasing until the vessels bifurcate (r' t). The reverse of this
holds true of those portions of the vessels which enter into the formation of
the sinuses of Valsalva (Plate XXVIII. fig. 18 i), these being unusually thin,
particularly where attached (?•)•* As the thickened portions of the vessels
correspond to the fixed margins of the segments (Plate XXVIII. figs. 17 and
35 btn), and extend between them in an arched direction above (c), they
give the precise boundaries of the sinuses of Valsalva (Plate XXVIII. figs.
17 and 18 d), and furnish the segments with three fibrous frameworks analogous,
in some respects, to the thickenings which occur in similar situations in the
veins. These frameworks extend for a, short distance into the segments (Plate
XXVIII. fig. 17 b, and fig. 36 n), and assist not only in affording the segments

* The several points adverted to are seen to advantage in the whale (Physalus antiquorum,
Gray), the aorta of which I had an opportunity of dissecting for the Museum of the Royal College
of Surgeons of England.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA.

771

the requisite degree of support, but in carrying them away from the sides of the
vessel, and in inclining them towards each other at such an angle as insures that
their free margins, especially where they unite above (Plate XXVIII. fig. 36 b c),
shall be more or less parallel when the valve is in action. That the frame-
works afford the support here indicated, is proved by the fact, that when liquid
plaster of Paris is introduced into the ventricles, and forced through the pul-
monary artery and aorta, in the direction of the circulation, the attached borders
of the segments do not fall back into the sinuses of Valsalva (Plate XXIX.
figs. 50 and 51 vw) to the same extent as the sides and free margins, but project
so as to furnish the casts thus obtained, with corresponding depressions (rs).
The sinuses of Valsalva are formed above by the dilatations or expansions
of the great vessels, and the one occupies a higher position than either of the other
two. They are further unequal in size (Plate XXVIII. fig. 26 w x v\ the
highest and smallest occurring anteriorly, that which is intermediate in size being
placed posteriorly, while the lowest and largest is directed towards the septum.
They correspond in situation and dimensions to the segments behind which they
are found, and differ from the venous sinuses in being more capacious, a section of
the sinus and its segment (which is likewise very ample) giving a sweep of nearly
half a circle (Plate XXVIII. fig. 18 b i s). As a result of this amplitude, those
portions of the segments which project into the vessel are, during the action of
the valve, closely applied to each other throughout a considerable part of their
extent (Plate XXVIII. fig. 26 abc); the great size of the sinuses furnishing
an increased quantity of blood for pressing the segments from above downwards,
and from without inwards, or in the direction of the axis of the vessel. The
sinuses of Valsalva curve towards each other in a- spiral direction • and this ought
to be attended to in speaking of the action of the semilunar valves, as the sinuses
direct the blood spirally on to the mesial line of each segment (Plate XXVIII.
fig. 26 v w x), and cause the segments to twist and wedge into each other, as re-
presented at v 7v x of figs. 26, 27, and 28, Plate XXVIII. In order to determine
this point, I procured a fresh pulmonary artery and aorta, and after putting the
valves into position with water, caused an assistant to drop liquid plaster of Paris
into the vessels. The greater density of the plaster gradually displaced the
water, and I was in this way furnished with accurate casts of the sinuses and of
the valves. The segments of the semilunar valves, unlike the venous ones, are
almost invariably three in number.* They differ in size and in position, and
in this respect resemble the sinuses of Valsalva, to the inside of which they
are found. Thus the segment which is smallest is situated anteriorly, and
occupies a higher position than either of the others ; that which is second in

* Dr John Hughes Bennett speaks of a case in which four were present, but whether the addi-
tional segment was congenital, or the result of disease, is not easy to determine. "Principles and
Practice of Medicine," 1858, p. 550.

772 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

size being placed posteriorly, and a little lower than the anterior segment.
The remaining segment, which is the lowest, is directed towards the septum.
They are flexible, more or less opaque, very strong, and somewhat crescentic
in shape (Plate XXVIII. figs. 19 and 20). In structure, the semilunar valves
are intermediate between the venous and auriculo-ventricular ones. They
consist of a reduplication of the fine membrane lining the vessel, strengthened
by certain tendinous bands, and, as was first satisfactorily demonstrated by Mr
W. S. Savory, of a considerable quantity of yellow elastic tissue.* Some of the
older anatomists, among whom maybe mentioned Lancisci,! Senac,^: Morgagni,§
Winslow, || and CoorER,*j[ believed that they had detected the presence of car-
neous or muscular fibres ; but Haller,** and many since his time, have gravely
doubted the accuracy of their observations. Very recently, Mr MooREff has
figured two sets of muscular fibres, which he has termed according to their
supposed action, dilators and retractors; and Dr Monneret];]; has described
two similar sets, which, for like reasons, he has named elevators and de-
pressors. I have sought in vain for the muscular fibres in question, and am
inclined to think that when found, they have been mistaken for the tendi-
nous bands accidentally stained with blood. The tendinous bands have hitherto
been regarded as following three principal directions, — one band being said to
occupy the free margin, and to be divided into two equal parts by the nodulus or
Corpus Arantii, otherwise called Corpusculum Morgagni, and Corpus sesamoideum ;
a second band, proceeding from points a little above the middle of the segment,
and curving in an upward direction towards the Corpus Arantii; the third band,
which is the thickest, surrounding the attached border of the segment. A careful
examination of a large number of mammalian hearts, particularly those of man,
has induced me to assign to the semilunar valves a more intricate structure. In
a healthy human semilunar valve§§ taken from the pulmonary artery, the follow-
ing seems to be the arrangement. Proceeding from the attached extremities of
the segment above (Plate XXVIII. fig. 19 b, fig. 20 x, and fig. 29 a), and running
along its free margin, is a delicate tendinous band, which gives off still more delicate

* Purkinge and Raeuschel had detected elastic tissue in the Corpora Arantii, but knew nothing
of its existence throughout the other portions of the valves. Of its presence I have frequently satis-
fied myself.

f De motu Cordis.

£ Traite de la Structure de Coeur, livre i.
§ Adversaria Anatomica Omnia.

|| Exposition Anat. de la Structure du Corps Humain, p. 592
% Myotomia Reformata.

** Elementa Physiologiee. Liber iv. sect. 10.
ft Med. Gazette, March 8, 1850.
+ + Lancet, Dec. 29, 1850.

§§ It is very difficult to get a perfectly healthy human semilunar valve, especially if the patient
is at all advanced in years. Out of twenty adult hearts examined by me, nearly a half of that num-
ber had the valves abnormally thickened.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA.

773

slips (Plate XXVIII. figs. 20 and 29 r), to radiate in a downward and inward
direction, i.e. in the direction of the mesial line (Plate XXVIII. fig. 20 c) and body
of the segment. These fine slips interdigitate in the mesial line, and are attached
below to the uppermost of a series of very strong fibrous bands which occupy
the body of the segment (Plate XXVIII. figs. 20 and 29 s). In the interspaces
between the slips, the valve is so thin as to be almost transparent. Those portions
of the segments included within the delicate fibrous band, running along the free
margin and the uppermost of the stronger bands occupying the body, and which
are situated to the right and left of the mesial line, are somewhat crescentic in
shape (Plate XXVIII. fig. 20 r), and have, from this circumstance, been termed
lunula?. They do not form the perfect crescents usually represented in books, the
horns of the crescents directed towards the mesial line of the segment (Plate
XXVIII. fig. 20 c), being much broader than those directed towards the extremi-
ties, or where the segments unite above (Plate XXVIII. fig. 20 b). The object
of this arrangement is obvious. The crescentic portions referred to, are those which,
when the segment is folded upon itself during the action of the valve, are accu-
rately applied to corresponding and similar portions of the two remaining seg-
ments (Plate XXVIII. fig. 25 b b'). If, however, the lunula? had been symme-
trical, in other words, if they had terminated in well-defined horns towards the
mesial line, or where the segments fold upon themselves, then the union between
the segments in the axis of the vessel (Plate XXVIII. fig. 25 x), where
great strength is required, would have been very partial, and consequently very
imperfect.

Proceeding from the attached extremities of the segments at points a little
below the origins of the marginal band, and curving in a downward and inward di-
rection, is the first of the stronger bands (^Plate XXVIII. fig. 20 b). The band referred
to essentially consists of two portions, these splitting up into brush-like expansions
as they approach the mesial line (c), where they interdigitate and become strongly
embraced. Other and similar bands, to the extent of three (s) or four, usually the
latter number, are met with (Plate XXVIII. fig. 29 v), and as they all curve in a
downward and inward direction, and have finer bands running between them in a
nearly vertical direction, they suspend the body of the segment; so that when
water is poured upon it, the various parts of which it is composed, radiate from
the attached or convex border like a fan ; each band dragging upon that above it ;
the whole deriving support from the thickened convex border. The bands, -which
are thus six in number, are best seen on that aspect of the segments which is
directed towards the sinuses of Valsalva* They are thickest at their attached
extremities, where they interlace slightly, and are mixed up to a greater or less
extent with the pale, soft, flattened fibres, and elastic tissue of the central layer

* The surfaces of the segments directed towards the axis are perfectly smooth, and so facilitate
the onward flow of the blood.

VOL. XXIII. PART III. 9 X

774 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

of the vessel itself. They in this manner form a fibrous zone (Plate XXVIII. fig.
17 bn), which corresponds to the attached convex border of the segment, and
may be regarded as an expansion of the inner of the two divisions (Plate XXVIII.
fig. 17 t r) into which, as I formerly pointed out, the pulmonary artery and aorta
resolve themselves.

As the bands under consideration are exceedingly strong when compared with
those occurring in other portions of the segment; and project in an inward direc-
tion, or towards the axis of the vessel, when the preparation is sunk in water ;
their function, as ascertained from numerous experiments on the semilunar
valves of a whale {Physalus antiquorum, Gray), seems to be the following : —

1st, They carry the tody of the segment away from the sides of the vessel, and
incline the free margins towards each other, at such an angle, as necessitates the free
margins of neighbouring segments, being always more or less in apposition. In this
they are assisted by the thickened portion of the pulmonary artery (Plate XXVIII.
figs. 17 and 36 b n) which projects between the segments (Plate XXVIII. fig. 36
n n') where they unite above, and by the fibrous zones which correspond to the
convex border of each segment.

2d, The stronger fibres suspend the body of the segment from above, and permit
the reflux of blood to act more immediately upon the mesial line of each segment where
thinnest (Plate XXVIII. fig. 20 c), and where least supported ; to occasion that
characteristic folding of the segment upon itself, when the valve is in action.

Other bands, intermediate in thickness between those occupying the free
margin and the body of the segment, are found towards its lower portion (Plate
XXVIII. figs. 20 and 29 o). These bands cross and interdigitate to a greater or
less extent, and as their prevailing direction is from below upwards, are instru-
mental in keeping the lower portions of the segment, away from the sides of the
vessel. Each segment may therefore be described as consisting of three por-
tions— a superior and thinner portion, an inferior and thicker one, and a central
portion, which is the thickest of all. It ought also to be remarked that the three
portions of the segment corresponding to its mesial line, where the folding occurs
when it is in action, are comparatively thinner than the parts to either side of
the line in question. The varying thickness of the segments is well seen in the
semilunar valve of the whale (Plate XXVIII. fig. 29 a v n).

While the foregoing may be considered a literal description of a healthy
human semilunar valve, there are modifications to which it is necessary to direct
attention. Thus, in some instances, the band occupying the margin of the segment
splits up near its origin, as represented at Plate XXVIII. fig. 19 b, and maps out a
triangular portion (c). This portion is very thin, and contains delicate tendinous
fibres, which terminate in brush-shaped expansions towards the mesial line.
The remaining and stronger bands are similar to those already described, but the
difference in the thickness of the several portions of the valve, is not so marked.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 775

In other cases (Plate XXVIII. fig. 21), the marginal band not only splits up and
contains a fully developed Corpus Arantii (d), but gives off two or more well-
marked tendinous slips (a) which connect the free margin with the stronger or
central portion of the segment (i). Radiating from the Corpus Arantii as a
centre (Plate XXVIII. fig. 24 d), and proceeding along the free margin, I have
sometimes detected a series of hair-like fibres (e), which are apparently of use
in strengthening this the weakest portion of the segment. This is the more
probable, since other and similarly delicate fibres proceed from the attached
extremities in the direction of the Corpus Arantii. On other occasions, the
tendinous bands proceeding from the marginal one (Plate XXVIII. fig. 22 s) are
abnormally thickened (t), and terminate in brush-shaped expansions in the body
of the segment (v) ; the body under such circumstances, projecting in an upward
direction towards the Corpus Arantii (d). In such cases, those portions of the
valve (r r') which occur between the thickened bands proceeding from the mar-
ginal one, are exceedingly thin, and in some diseased conditions altogether awant-
ing, so that the segment very much resembles one of the segments of the mitral
or tricuspid valve, with its chordae tendineae. That there is an analogy between
the semilunar and the mitral and tricuspid valves, and that the chordae tendineae
is a further development, seems probable from the fact, that in the bulbus
arteriosus of certain fishes, as in the grey and basking sharks (Plate XXIX.
figs. 41 and 48), Lepidosteus, &c. (Plate XXIX. fig. 40 5), the semilunar valves
are furnished with what may be regarded as rudimentary chordae tendineae,
(Plate XXIX., fig. 48. «), while in the auriculo-ventricular valves of fishes, which
have hitherto been regarded as semilunar, but which exhibit some of the pecu-
liarities of the mitral valve of the mammal, chordae tendineae in various stages
of development occur.

A scheme of the arrangement of the tendinous bands in the semilunar valves
has been given at Plate XXVIII. fig. 23, and shows the segments to be not only
bilaterally symmetrical, but to be constructed on a plan which secures the greatest
amount of strength with the least possible material ; the bands mutually acting
upon and supporting each other. Thus the bands marked a and d, which re-
present the central portion of the segment, split up into brush-shaped expansions,
one portion of each curving in an upward direction (b e), and representing the
tendinous slips proceeding from the marginal one (r) ; the remaining portions
curving in a downward direction (/c), and giving the inferior set of fibres which
curve from below, towards the body of the segment (ad). The Corpus Arantii
is rarely present in a perfectly healthy semilunar segment ; nor will its absence
occasion surprise, when it is remembered that its presence materially interferes
with the folding of the segments upon themselves, when the valve is in action.
That its existence is not necessary to the perfect closure of the valve, is proved by
its complete absence in a great number of cases. In the semilunar valve of the

776 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

whale, where one would have naturally expected it in perfection, I could not
detect even a trace of it.

What has been said of the semilunar valves of the pulmonary artery, may with
equal propriety be said of those of the aorta ; the only difference being that the
segments are stronger and more opaque, to harmonise with the greater strength
of the left ventricle.

The Arterial or Semilunar Valves in Action.

As the manner in which the semilunar valves are closed, does not seem to be
well understood, the following experiments conducted with various fluids and
liquid plaster of Paris, may prove interesting : —

When the aorta is cut across two inches or so above the aortic semilunar
valve, and water introduced, the segments, if watched from beneath, are seen to
act with great alacrity, the smallest segment (Plate XXVIII. figs. 26, 27, and 28,
w), which is situated highest, descending with a spiral swoop, and first falling into
position ; the middle-sized segment (a*), which is placed a little lower, descending
in like manner, and fixing the first segment by one of its lunulas or crescentic surfaces
(Plate XXVIII. fig. 26 a) ; the third and largest segment (v>), which occupies a
lower position than either of the others, descending spirally upon the crescentic
margins (b c) of the other two, and wedging and screwing them more and more
tightly into each other. The spiral movement, as has been already explained, is
occasioned by the direction of the sinuses of Valsalva, which curve towards each
other, and direct the blood in spiral waves upon the mesial line of each segment
(wxv).

It is well seen when liquid plaster of Paris is used, as the plaster, on setting,
enables the experimenter to examine the relations of the segments to each other
at leisure. Figures 27 and 28, Plate XXVIII, have been taken from specimens so
prepared. On removing one of the segments in such specimens, it is found to be
folded upon itself (Plate XXVIII., fig. 27 w), and to present two semilunar surfaces,
each of which is accurately applied to a corresponding and similar surface of that
segment of the valve which is next to it (Plate XXVIII. fig. 25 b b'). The union,
therefore, between any two of the segments of a semilunar valve, is analogous in
many respects, to that occurring in a venous valve consisting of two segments.
There is, however, this difference ; in a venous valve, the segments, simply flatten
themselves against each oth er in th e mesial -plane of the vessel, to form a perpendicular
crescentic wall (Plate XXVIII. figs. 11 and 13 e) ; whereas in thes emilunar valves,
the segments in addition curve into each other, and so form three perpendicular
crescentic walls, each of which radiates from the axis of the vessel (Plate XXVIII.
fig. 26 rso). In the venous valve, moreover, those portions of the segments
which come into apposition form systemetrical crescents (Plate XXVIII. fig. 13 e) ;

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 777

whereas in the semilunar one, the surfaces referred to, are non-symmetrical; in
other words, the horns of the crescents forming the lunulse, are broader towards the
mesial line of the segments (Plate XXVIII. fig. 20 cy than where they meet above
(b). As a result of this want of symmetry in the lunulse or opposing surfaces of
the semilunar valves, the apices or central portions of the segments come together
in the axis of the vessel throughout a considerable space (Plate XXVIII. fig. 25 x),
and form a union of the most perfect description. The extent of the union increases
in the inverse of the pressure applied (compare dotted lines, Plate XXVIII. fig.
25 m m' with plain ones b b'), and is rendered very secure from the segments
being wedged into each other in a direction from above downwards and from with-
out inwards (Plate XXVIII. fig. 26 vwx). Retzius,* who figures the manner
of closure of the semilunar valves, does not seem to have been aware of this fact,
for he represents the segments as coming together in the axis of the vessel at
three points, an arrangement which could scarcely fail to occasion a certain
amount of regurgitation. If the closure of the semilunar valves be watched from
above, other phenomena are observed. When, for example, the aorta and semi-
lunar valve of the whale were sunk in water and permitted to remain un-
disturbed, the thicker portions of each segment were seen to project in an upward
and inward direction, the free margins being by this arrangement brought more
or less closely into contact, and supported on a level corresponding to the top of
the sinuses of Valsalva. When, however, the preparation was raised in the
vessel, so that the water acted from above on the central and more unsupported
portions of the segments ; the free margins, together with the more moveable parts
of the bodies, descended to the extent of fully an inch and a half. In so doing,
the free margins of the segments were projected against and accurately applied
to each other, clearly showing that the fluid, because of its weight and the spiral
downward and inward direction communicated to it by the sinuses of Valsalva,
is sufficient to effect the closure. When the closure was taking place, the seg-
ments fell into position in rotation, but at so nearly the same interval of time,
that they mutually regulated the amount of downward and inward movement ;
and so prevented each other from protruding too far into the interior of the vessel.
When the hand was introduced into the aorta, which the great size of the speci-
men! readily permitted, and one of the segments was pushed in an outward
direction, it was found to apply itself to the sinus of Valsalva behind it, with
more or less accuracy ; the extremities of the segments, where they unite above,
projecting to form three ridges, which are spirally inclined with reference to each
other, and are no doubt useful in directing the blood into the aorta proper. From
the foregoing description of the venous and arterial semilunar valves in mam-

* Om Mekanismen af Semilunar Valvlernes tillolutning.

t In this case, the aorta had a girt of 27 inches ; the average size of the segments being
9 inches by 7.

VOL. XXIII. PART III.

778 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

malia, it will be evident that there is nothing, either in their structure or rela-
tions, to betoken any great degree of activity on their part. That these structures
are, on the contrary, principally passive, seems certain from the fact, that a
stream of water or other fluid directed upon them from above as recommended,
at once closes the orifices which they guard.

Structure of the Bulbus arteriosus of the Fish, and of the Ventricle of the Fish
and Eeptile ; Semilunar and other Valves found therein.

The semilunar valves in the bulbus arteriosus of the fish, and the auriculo-ven-
tricular valves in the fish and reptile, differ from the venous and arterial ones,
in being, for the most part, connected either directly or indirectly, or exposed in
some way to the influence of muscular contractions. In order the better to
understand the position which these valves occupy in the gradually ascending
scale of valvular arrangements, a brief description of the bulbus arteriosus, of
the fish, and of the ventricle of the fish and reptile, is necessary. In the ventricle
of the fish, the fibres, as I have pointed out elsewhere,* consist of three layers ; —
an external layer, in which they proceed from base to apex, and occasionally
interdigitate and become strongly embraced ; an internal layer, in which they
are aggregated into fascicular bundles, and have a more or less vertical reticu-
lated arrangement ; and a central layer, in which they run transversely, or at
right angles to the fibres of the external and internal layers. These layers are
connected to each other by certain fibrous bands, which run in a direction from
without inwards. Rising from the base of the ventricle anteriorly is a muscu-
lar structure of a more or less bulbous form, the so-called bulbus arteriosus
(Plate XXIX. figs. 38, 39, 40, 41, and 48), the arrangement of the fibres in
which, resembles that in the ventricle itself. The ventricle of the fish, and
the bulbus arteriosus contract in every direction, and in this respect they are
analogous to the veins and arteries, which, as John Hunter showed, are exten-
sible and retractile, both in their length and breadth. One point to be noted in
the ventricle of the fish, is the absence of musculi papillares ; the auriculo- ventri-
cular valves being so placed, that certain of the fasciculi constituting the internal
layer, run parallel to them, and extend, in not a few instances, into their sub-
stance. The effect of this arrangement is to modify the action of the valves in
question ; and I direct attention to the circumstance, because of the purely
mechanical views entertained by some with regard to them ; views which to me
appear inconsistent with the nature of the textures involved. The arrangement
of the fibres in the ventricle of the reptile is nearly the same as that in the
fish. There is, however, this difference, and it is worthy of mention as bearing
directly upon the structure and function of the auriculo- ventricular valves in this

* On the Arrangement of the Muscular Fibres, in the Ventricles of the Vertebrate Heart, with
Physiological Remarks. — Phil. Trans., vol. 154, pp. 445-47.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 779

class of animals. The fibres of the external and internal layers pursue a slightly
spiral course. The spiral direction of the fibres here indicated is so marked in
the ventricles of the bird and mammal, as to influence not only the position of the
musculi papillares and carnese columns, but also the shape of the ventricular
cavities, and the closure of the mitral and tricuspid valves. In the bulbus
arteriosus of the fish, the valves as a rule, may be said to be fairly within the
range of muscular influence, and it is interesting to note that in this struc-
ture, the segments vary both as regards number, size, and shape. Thus,
in the frog-fish (Lophius piscatorius), the origin of the bulbus arteriosus is
guarded by a semilunar valve, consisting of two ample and very delicate
segments (Plate XXIX. fig. 47 a), resembling those found in the middle-sized
veins (Plate XXVIII. fig. 3 ; compare with a b) ; while in the sun-fish (Orthago-
riscus mola, Schneider), the same aperture is guarded by a semilunar valve, con-
sisting of three segments (Plate XXIX. fig. 43 a b c) ; the segments being analo-
gous in every respect to those found in the largest veins (Plate XXVIII. fig. 1 ;
compare with a b c). As the valve in these cases is situated between the bulbus
arteriosus and the ventricle, and surrounded by a fibrous ring similar to that occur-
ring at the origin of the pulmonary artery and aorta, it is not affected by the struc-
tures between which it is situated to any great extent. The semilunar valves in
the frog-fish and sun-fish, may therefore be regarded as connecting links between
the venous and arterial ones in the bird and mammal ; and that more complex
system of analogous valves, which is found in the bulbus arteriosus of the fish
generally. In the bulbus arteriosus of the skate [Raid batis), the segments occupy
the whole of the interior of the bulb, and are arranged in three pyramidal rows
of five each (Plate XXIX. fig. 38 a be). As the segments in this instance are
very small, and altogether inadequate to the obliteration of the bulbus cavity, they
must be looked upon as being useful only in supporting the column of blood in its
onward progress ; it being reserved for the segments at the termination of the bulb,
which are larger and more fully developed, to effect the closure. The action of
the segments in the bulbus arteriosus of the skate, is rendered more perfect by the
pressure from without, caused by the contraction of the bulb itself (d). In the
bulbus arteriosus of the sturgeon {Accipenser sturio), the segments are arranged in
three rows of eight each (Plate XXIX. fig. 39 a). They are more delicate, and less
perfectly formed than in the skate. In the bulbus arteriosus of the American
devil-fish (Cephalopterus giorna), they increase to thirty-six, are more imperfect
than in any of the others, and are supported by three longitudinal angular mus-
cular columns. As these segment-bearing columns, from their shape, project
into the cavity, so as almost to obliterate it during the contraction of the bulb,
they in this way bring the free margins of the segments together. The orifices of
the bulbus arteriosus, however, are not closed by the imperfect segments referred
to ; these being guarded by two well-formed and fully developed tri-semilunar

780 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

valves, the one of which is situated at the beginning, the other at the ter^
mination of the bulb. In the bulbus arteriosus of the grey shark [Galeus
communis", we have a slightly different arrangement, the two rows of segments
of which the valve is composed being connected to each other by means of
tendinous bands, resembling chordse tendinese (Plate XXIX. fig. 48 a). In
the bulbus arteriosus of the Lepidosteus (Plate XXIX. fig. 40 b), and that of the
basking shark (Selachi maxima, Cuv.), (Plate XXIX. fig. 41 b), the same arrange-
ment prevails ; the segments being stronger and less mobile, and the tendinous
bands which bind the one segment to the other, more strongly marked than in
the grey shark. As the tendinous bands referred to are not in contact with the
wall of the bulbus arteriosus, but simply run between the segments, and are in
some instances, as in the basking shark, very powerful (Plate XXIX. fig. 41 b),
they must be regarded in the light of sustaining or supporting structures ; their
function being probably to prevent eversion of the segments. Other examples
might be cited, but sufficient have been adduced to show, that the nature, as well
as the number and arrangement of the segments, is adapted to the peculiar
wants of the structure in which they are situated ; and it ought not to be over-
looked, that when a multiplicity of segments are met with in an actively con-
tracting organ, the two act together or in unison.

If we now direct our attention to the auriculo-ventricular valves of the fish
and reptile, similar modifications as regards the number of the segments, and
the presence or absence of chordae tendinese and analogous structures, pre-
sent themselves. Thus in the heart of the serpent {Python tigris), the two
crescentic apertures by which the blood enters the posterior or aortic division
of the ventricle, are each provided with a single semilunar valve. The same
may be said of the aperture of communication, between the left auricle and
ventricle of the crocodile (Crocodilus acutus) and of the sturgeon (Accipenser
sturio, Linn.) In the heart of the Indian tortoise (Testudo Indica, Vosmaer),
the left auriculo-ventricular orifice is guarded bp a single membranous fold, the
right orifice having in addition a slightly projecting semilunar ridge, which ex-
tends from the right ventricular wall, and may be regarded as the rudiment
of the fleshy valve which guards the same aperture in birds (Plate XXIX. fig.
45 gli). In the heart of the bulinus, frog-fish, American devil-fish, grey shark,
and crocodile, the auriculo-ventricular orifice is guarded by a semilunar valve
consisting of two cusps or segments ; while in the sturgeon, sun-fish, and others,
it is guarded by four, two larger and two smaller.

So much for the number of the segments constituting the auriculo-ventricular
valves in fishes and reptiles ; but there are other modifications which are not
less interesting physiologically. In the bulinus, frog-fish, and crocodile, the
segments of the valves are attached to the auriculo-ventricular tendinous ring,
and to the sides of the ventricle, and have no chorda? tendinece. In the sun-fish

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 781

(Plate XXIX. fig. 43 /), the valve is destitute of chordae tendinese likewise ; but in
this instance the muscular fibres are arranged in the direction of the freemarginof
the segments of the valve, and no doubt exercise an influence upon them. In the
grey shark the membranous folds forming the segments, are elongated at the
parts where they are attached to the ventricular walls, these elongated attach-
ments being more or less split up, so as to resemble chorda? tendinew.

In the American devil-fish the semilunar valve consists of two strong well-
developed membranous folds, which, like the preceding, are attached by elongated
processes to the interior of the ventricular wall ; these processes consisting of dis-
tinct tendinous slips, which are attached to rudimentary musculi papillares.

In the sturgeon (Plate XXIX. fig. 37), three tendinous chords (b) from
rudimentary musculi papillares, are seen to extend into the half of each of
the segments ; while in the left ventricle of the dugong, six chords, proceeding
from tolerably well-formed musculi papillares, are distributed to the back, and
six to the margins of each of the segments. It is, however, in the bird and
mammal, particularly the latter, that the musculi papillares are most fully de-
veloped, and the chordse tendinese most numerous — the number of tendinous
chords, inserted into each of the segments, amounting to eighteen or more (Plate
XXVIII. fig. 33 rr', ss'). As the auriculo-ventricular valves are attached either
to the interior of the ventricle, or to the musculi papillares or carnese columnse,
it is plain that the contraction of the ventricle must influence them to a greater
or less extent. That, however, the presence of muscular substance in no way
interferes with the efficiency of the valves, is proved by the fact, that some valves
are partly muscular and partly tendinous, a few being altogether muscular. Thus,
in the heart of the cassowary, the right auriculo-ventricular orifice is occluded by
a valve, which is partly muscular and partly tendinous ; the muscular part, which
is a continuation of two tolerably well-formed musculi papillares, extending into
the tendinous substance of the valve, where it gradually loses itself. In the
right ventricle of the crocodile (Plate XXIX. fig. 42 r), a muscular valve, resem-
bling that found in the right ventricle of birds, exists.

In birds the muscular valve (Plate XXIX. figs. 45 and 46 g h i) is usually
described as consisting of two parts, from the fact of its dependent or free
margin (g) being divided into two portions by a spindle-shaped muscular band
(h), which connects it with the right ventricular wall (J). As, however, the wall
consists of one continuous fold towards the base (i), and the two portions of the
margin are applied during the systole not to each other but to the septum
(ef e' O) it is more correct to say that the valve is single ; the spindle-shaped mus-
cular band representing the musculus papillaris of the right wall of the ventricle
with its attached chordse tendinese.* In the serpent, the opening between the right

* For the relations, structure, and function, of the muscular valve in birds, see paper already
referred to. Phil. Trans, vol. 154, pp. 470-1-2.

VOL. XXIII. PART III. 9 Z

782 DR PETTIGREYV ON THE RELATIONS, STRUCTURE, AND FUNCTION,

and left ventricle, occurs as a spiral slit in the septum (Plate XXIX. fig. 44 r), and
is guarded by two projecting muscular surfaces, which are rounded off for this
purpose. The opening into the left ventricle also occurs as a muscular slit (s) ;
and the orifices of many of the venous sinuses are closed by purely muscular adap-
tations ; the fibres in such instances running parallel to the slit-like opening (Plate
XXVIII. fig. 10), and being continuous with two or more bundles of fibres (b c),
which supply the place of musculi papillares. From the great variety in the
shape and structure of the auriculo- ventricular valves, and from the existence in
almost all of tendinous chords, which connect them with actively contracting
textures, there can, I think, be little doubt, that they possess an adaptive power
peculiar in a great measure to themselves ; this power being traceable to the
contractile properties residing in muscle.

As it would greatly exceed the limits of the present paper, to give a detailed
account of the structure of the numerous auriculo-ventricular valves, to which
allusion has been made, I have selected for description the auriculo-ventricular
valves of the mammal, and those of man more particularly. Before, however,
entering upon this the most difficult part of the present investigation, a brief
account of the arrangement of the muscular fibres in the ventricles seems indis-
pensable ; these, as has been explained, modifying the action of the valves to a
very considerable extent.

Arrangement op the Muscular Fibres in the Ventricles of the Mammal — Shape of

the Ventricular Cavities, &c.

The fibres of the ventricles in the mammal, as I have ascertained from
numerous dissections,* are arranged in seven layers; three external, a fourth or
central, and three internal. The fibres constituting these layers in the left ven-
tricle, to which these remarks more particularly apply, pursue a spiral direction ;
the external fibres becoming more and more oblique, in a direction from left to
right downwards, as the central layer is approached — the internal fibres becoming
more and more vertical, in a direction from right to left upwards, as it is receded
from. The fibres, therefore, of corresponding external and internal layers, cross
each other. The fibres of the several layers are further arranged in two sets ; the
two sets, forming each of the external layers, being continuous at the apex and
at the base, with two similar sets belonging to a corresponding internal layer.
This arrangement of the fibres renders the ventricles bilaterally symmetrical, and
in part accounts for the great precision with which the heart acts, and for its roll
ing movements. Its bearing on the action of the organ is obvious, for as muscular
fibres contract in the direction of their length, the more vertical external and
internal fibres, diminish the ventricular cavities from above downwards, and from

* Of these upwards of an hundred are preserved in the University of Edinburgh Anatomical
Museum, where they may be examined. For a detailed description of the specimens, and for
accurate representations thereof, see Phil. Trans, vol. 154, pp. 445-500, Plates 12 to 16.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 783

below upwards ; the downward movement preceding the upward by an almost
inappreciable interval of time. In that brief space, however, which elapses
between the downward and upward movements, the ventricles, owing to the
contraction of the more circular fibres, are visibly diminished from without in-
wards ; and it is important to note this circumstance, as the auriculo-ventricular
orifices are, at this instant, reduced in size, and the mitral and tricuspid valves,
consequently liable to a certain amount of displacement. The ventricular wall
of the left ventricle, as was known to Gerdy and other investigators, is thickest at
the upper part of its middle third (Plate XXVIII. fig. 35/), and tapers towards the
apex (w) and base (v') respectively ; and it is interesting to observe that the thickest
part of the ventricular wall, corresponds with the widest portion of the ventricular
cavity, whence the blood is projected into the aorta; a fact of some significance,
since the contractions at this point are necessarily more intense than at any other.
As the two sets of fibres composing the first external layer are continuous at the
left apex with the two sets of fibres forming the carnese columnse and musculi
papillares, and these structures, especially the latter, bear an important relation
to the segments of the bicuspid valve, with which they are connected by the
chordae tendinese, a more minute, description than that given of the other layers,
is requisite for clearness. On looking at the left auriculo-ventricular opening
(Plate XXVIII. fig. 30 b), the fibres of the first layer are seen to arise from
the fibrous ring surrounding the aorta {a), and from the auriculo-ventricular tendi-
nous ring (n) in two divisions; the one division (d) proceeding from the anterior
portions of the rings, and winding in a spiral nearly vertical direction, from before
backwards, to converge and enter the apex posteriorly ; the other set (Plate XXVIII.
fig 30 /) proceeding from the posterior portions of the rings, and winding in a
spiral direction from behind forwards, to converge and enter the apex anteriorly.
Having entered the apex, the two sets of external fibres are collected together,
and form the musculi papillares and carnese columnse; the one set, viz., that
which proceeded from the auriculo-ventricular orifice anteriorly and entered the
apex posteriorly, curving round in a spiral direction from right to left upwards, and
forming the anterior musculus papillaris (Plate XXIX. fig. 50 y), and the carnew
columnce next to it; the other set, which proceeded from the auriculo-ventricular
orifice posteriorly, and entered the apex anteriorly, curving round in a correspond-
ing spiral direction, and forming the posterior muscidus papillaris (Plate XXIX.
figs. 50 and 51 x), and adjoining carnew columnce. As the external fibres con-
verged on nearing the apex, so the internal continuations of these fibres radiate
towards the base; and hence the conical shape of the musculi papillares. I am
particular in directing attention to the course and position of the musculi papil-
lares, as they have hitherto, though erroneously, been regarded as simply vertical
columns, instead of more or less vertical spiral columns* The necessity for in-

* Plate XXIX. fig. 49, x y, gives the spiral track of the musculi papillares.

784 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

sisting upon this distinction will appear more evident when I come to speak of the
influence exerted by these structures on the segments of the bicuspid valve. It is
worthy of remark, that while the left apex is closed by two sets of fibres, the left
auriculo-ventricular orifice is occluded during the systole by the two flaps or seg-
ments constituting the bicuspid valve (Plates XXVIII. and XXIX. figs. 28 and 51
m n). The bilateral arrangement, therefore, which obtains in all parts of the ven-
tricle and in the musculi papillares, extends also to the segments of the valve in
question. What has been said of the arrangement of the fibres in the left ventricle,
applies with slight modifications to the fibres of the right one ; and many are of
opinion (and I also incline to the belief) that the tricuspid valve, is in reality bicus-
pid in its nature (Plate XXVIII. fig. 34 m n ; and Plate XXIX. fig. 51 g'h). The
shape of the ventricular cavities of the heart of the mammal greatly influences the
movements of the mitral and tricuspid valves, by moulding the blood into certain
forms, and causing it to act in certain directions. It is seen to advantage when the
ventricles are filled with wax or plaster of Paris, and, the ventricular parietes re-
moved to expose the casts or moulds thus obtained (Plate XXIX. figs. 50 and 51).

The form of the left ventricular cavity, which I regard as typical, is that of a
cone twisted upon itself (Plate XXIX. fig. 49) ; the twist or spiral running from
left to right of the spectator, and being especially well marked towards the apex.*
The cone tapers slightly towards its base (b), and the direction of its spiral corre-
sponds with the direction of the fibres of the carnese columnse and musculi
papillares (Plate XXIX. fig. 50 xy). As the two spiral musculi papillares project
into the ventricular cavity, it follows that between them, two conical- shaped
spiral depressions or grooves, are found (Plate XXIX. fig. 49 qj). These grooves,
which are especially distinct, are unequal in size ; the smaller one (Plate XXIX.
figs. 49 and 50 j) beginning at the right side of the apex, and winding in an up-
ward spiral direction, to terminate at the base of the external or left and smaller
segment of the bicuspid valve (Plate XXIX. figs. 50 apd 51 n) ; the larger groove
(Plate XXIX. fig. 49 q) beginning at the left side of the apex, and pursuing a
similar direction, to terminate at the base of the internal or right and larger seg-
ment (Plate XXIX. fig. 51 m).

Running between the grooves in question, and corresponding to the septal
aspect of the ventricular cavity, is yet another groove, larger than either of the
others (Plate XXIX. fig. 51 q). The third or remaining groove winds from the
interior of the apex posteriorly, and conducts to the aorta (a), which, as the reader
is aware, is situated anteriorly. The importance of these grooves physiologically
cannot be over-estimated, for I find that in them the blood is arranged or
moulded into three spiral columns, and that towards the end of the diastole and
the beginning of the systole, the blood in the two lesser ones is forced in two
spiral streams upon the segments of the bicuspid valve, which are in this

* In this description the heart is supposed to be placed on its apex.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 785

way progressively elevated towards the base, and twisted and wedged into each
other, until regurgitation is rendered impossible (Plate XXIX. fig. 51 m n). When
the bicuspid valve is fairly closed, the blood is directed towards the third
and largest groove, which, as has been stated, communicates with the aorta. The
spiral action of the mitral valve, and the spiral motion communicated to the blood
when projected from the heart, is due to the spiral arrangement of the musculi
papillares and fibres composing the ventricle, as well as to the spiral shape of the
left ventricular cavity. These points are determined in the following manner : —
When a cast of the interior of the left ventricle is made, by introducing liquid
plaster of Paris into the left ventricular cavity, by means of a tube inserted
into the aorta and reaching to the left apex, it is found, on cutting away the
parietes of the ventricle, that the segments of the mitral valve are borne up on
the plaster,* and wedged into each other on a level with the ventricular orifice.
It is further found, that the two spiral streams of plaster (now spiral columns)
which closed the segments of the mitral valve, merge towards the base, into
the third column, communicating with the aorta. That portion, therefore, of the
left ventricular cavity (Plate XXIX. figs. 50 and 51 o), which corresponds to the
conus arteriosus or infundibulum of the right one (Plate XXIX. fig. 50 i), is
conical in form. It is moreover furnished with three conical-shaped spiral
depressions, which in the cast appear as conical-shaped spiral prominences {p o),
and are continuous with the three spiral columns of plaster proceeding from the
apex of the ventricle. As the apices of the three conical-shaped infundibuliform
prominences referred to are directed between the three segments of the aortic
semilunar valve, the blood from this arrangement must on its onward progress
throw the semilunar segments hastily apart, by causing them to fall back upon the
spirally disposed sinuses of Valsalva wv). The spiral channel, which is thus
provided for the blood, is not confined to the heart, but extends for a short distance
into the great vessels. As the semilunar valves are closed by a reverse move-
ment to that by which they are opened, it is not difficult to perceive how the
spiral action of the segments constituting them is induced.

What has been said of the left ventricular cavity and aorta, applies, with slight
alterations, to the right ventricular one and the pulmonary artery (Plate XXIX.
figs. 50 and 51 ci), the cone formed by the right cavity being flattened out and
applied to or round the left.

Intricate Structure of the Mitral and Tricuspid Valves in Mammalia ; Eelations of
the cord^e tending to the segments and to the musculi papillares.

The auriculo-ventiicular valves are composed of segments, which differ in
size, and are more or less triangular in shape. They are much stronger than

* In order to see the spiral movement of the segments to advantage, the plaster ought to he
made very thin. Should any difficulty occur, the experimenter is recommended to use water until
he is familiar with the phenomena to be observed.

VOL. XXIII. PART III. ] 0 A

786 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

the segments of the semilunar valves, which in some respects they resemble
in structure as well as function. They are very dense, and quite opaque,
unless at the margins and apices, where they are frequently remarkably thin.
They unite at the base where thickest, to form a ring, which is attached to
one or other of the fibrous rings surrounding the auriculo-ventricular orifices
(Plate XXVIII. fig. 30 nri). The auriculo-ventricular rings, which are consequently
intimately related to the segments, have been variously described, the majority
of investigators regarding them as highly developed structures, which afford
attachment, not only to the valves, but to all the fibres of the auricles and
ventricles. A careful examination of the rings in question in boiled hearts,
has led me to a different conclusion. They afford attachment to the fibres of
the auricles (Plate XXVIII. fig. 35 yd), and to the valves (mn), but to almost none
of the fibres of the ventricles (v). They are most fully developed anteriorly, and on
the septum, where they form a dense fibrous investment. The left ring, like
everything else pertaining to the left ventricle, is more fully developed than the
right ; but neither the one nor the other can compare in breadth, or thickness,
with either of the arterial rings (ak). The influence, therefore, which they exert on
the dilatation and contraction of the auriculo-ventricular orifices (Plate XXVIII.
fig. 30 bl) must be immaterial. The position of the segments in the auriculo-ven-
tricular orifices, and their relation to the musculi papillares, is deserving of atten-
tion. On looking into the auriculo-ventricular orifice of the left or typical ven-
tricle, when the clots which usually fill the ventricular cavity have been removed,
it is found to be partially obliterated, by two principal segments ; the one of which
is larger than the other (Plate XXVIII. fig. 28 m). The larger segment, which is
obliquely suspended between the auriculo-ventricular and aortic openings, occupies
a somewhat internal and anterior position ; while the smaller one [n), which runs
parallel to it, occupies a more or less external and posterior position. Between
the principal segments, two smaller accessory segments, are usually found. In
the right ventricle, the principal segments are three in number, and are of dif-
ferent sizes, — the smallest running parallel to the septum ; the largest being
placed anteriorly and inclined to the right side ; the one which is intermediate in
size occupying a more posterior position. These, also, have smaller accessory
segments placed between them. The segments, whatever their size, are attached
by their bases to the auriculo-ventricular tendinous rings (Plate XXVIII. fig. 30
n n'), and, by their margins and apices, to the spiral musculi papillares (Plate
XXVI II. fig. 28 abed), by means of the chordae tendineae.

The segments of the mitral valve, to which the following description, drawn
from an extensive examination of mammalian hearts,* more particularly applies,

* Of the hearts examined may he mentioned those of man, the elephant, camel, whale (Physalus
antiquorum, Gray), mysticetus, horse, ox, ass, deer, sheep, seal, hog,, porpoise, monkey, rabbit, and
hedgehosr.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 787

consist of a reduplication of the endocardium, or lining membrane of the heart,
containing within its fold, large quantities of white fibrous tissue, and, as was
pointed out by Mr W. S. Savory, and after him, by Professor Bonders,* of a
moderate amount of yellow elastic tissue. The white fibrous tissue greatly pre-
ponderates, and is derived principally from the chordae tendinese, which split up
into a vast number of brush-shaped expansions, prior to being inserted into the
segments. The fibrous or tendinous expansions, which assume the form of bands,
may consequently be regarded as prolongations of the chordae tendinese. They are
analogous, in many respects, to similar bands in the semilunar valves ; the only
difference being, that in the semilunar valves, the bands referred to, instead
of being free, as in the present instance, are involved in the valvular substance.
(Compare fibrous bands marked in Plate XXVIII. fig. 20, with chordae tendineae
and brush-shaped expansions, marked s in Plate XXVIII. fig. 33). As each
of the segments composing the bicuspid or mitral valve, like the left ventricle
itself, is bilaterally symmetrical, it Avill be convenient, when speaking of
these structures, to describe, in the first instance, only the half of one of
the segments; and in order to do this the more effectually, it will be neces-
sary to consider each musculus papillaris, as essentially consisting of two
portions ;f a superior and external portion (Plate XXVIII. figs. 28 and 33 «),
which gives off two, usually three chordae tendineae (s) to that half of the anterior
segment of the mitral valve (m) which is next to it ; and an inferior and internal
portion (b), which also gives off three tendinous chords ; these being inserted into
the adjacent half of the posterior segment (n). The three tendinous chords which
proceed from the superior external portion (Plate XXVIII. fig. 31 r), subdivide,
and are inserted, by the brush-shaped expansions spoken of, into the half of
the anterior segment posteriorly, in nine different places, j Of these, three are
inserted into the mesial line of the segment (Plate XXVIII. figs. 31, 32, and
33, r), viz., into the base (g), central portion (/), and apex (e) ; three into the
basal, central, and apicial portion of the free margin (Plate XXVIII. fig. 33 s') ;
and three into intermediate points between the mesial line and the margin
(/). On some occasions, as in the mitral valve of the whale, a slightly different
arrangement prevails ; three chordse tendineae being inserted into the mesial line
of the segment at the base, at the centre, and at the apex ; an additional chord
going to the free margin near the apex ; three into intermediate points between
the mesial line and the margin ; a second additional chord going to the central

* Professor Donders describes the yellow elastic tissue as being most abundant in the upper
surface of the segments.

\ The musculi papillares in the human and other hearts (Plate XXVIII. figs. 28, 31, and 33
ab, erf) either bifurcate, or show a disposition to bifurcate at their free extremities, so that the division
of the chordse tendineae into two sets is by no means an arbitrary one.

I The number of insertions vary in particular instances. In typical hearts, however, it is re-
markably uniform.

788 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

portion of the margin. A third and independent chord, goes to the base of the
margin. In the whale, as will be observed, the arrangement is virtually the
same as that first given ; the insertions being nine in number, — three into the
mesial line, three into the free margin, and three into intermediate points.
The tendinous chords pursue different directions prior to insertion ; the three
which are inserted into the mesial line of the segment, and are the longest
and strongest (Plate XXVIII. figs. 31, 32, and 33 r), being less vertical
than those which are inserted nearer the margin (V) ; these in turn being
less vertical than the ones inserted into the margin, which are the shortest
and most delicate. The basal chord of each set, on the contrary, is more
vertical than that beneath it, or nearer the apex (x) ; the apicial chords being-
more or less horizontal. As there is a disposition on the part of the higher
and more central chordae tendinese (Plate XXVIII. fig. 31 g) to overlap, by their
terminal brush-shaped expansions, those below and to the outside of them, the
segment is found to diminish in thickness from the base {z) towards the apex (x)
and from the mesial line towards the periphery or margin ; the basal and central
portions of the segment being comparatively very thick, the apicial and marginal
portions very thin (Plate XXVIII. fig. 32 vx); so thin, indeed, that in some
hearts, particularly in the right ventricle, they present a cobwebbed appearance.
As the marginal portions form the counterparts of the lunulas in the semilunar
valves, and are those parts of the segments which come into accurate apposition
when the valve is in action, they are, from this circumstance, entitled to con-
sideration. When a perfectly healthy mitral valve from an adult, or, still
better, from a foetus at the full time or soon after birth, is examined, the
portions referred to are found to be of a more or less crescentic shape {vide
that part of the mitral valve to which the chordae tendinese marked rJ, fig.
33, Plate XXVIII., are distributed), and so extremely thin, that the slightest
current in the fluid in which they are examined causes them to move like
cilia9. The physiological value of this delicacy of structure, and consequent
mobility, is very great ; as the most trifling impulse causes the marginal parts
of the segments, which are naturally in juxtaposition, to approach towards
or recede from each other. The half of one of the segments of the mitral
valve may be regarded as consisting of a reduplication of the endocardium or
lining membrane of the heart, supported or strengthened in all directions by nine
or more tendinous brush-shaped expansions; these expansions being arranged
in three vertical rows of three each (Plate XXVIII. fig. 33), with much pre-
cision, and according to a principle which is seldom deviated from. In addition
to the reduplication of the lining membrane and the tendinous expansions re-
ferred to, Lancisi,* Senac,j and Kurschner^ have ascertained that there is a

* De Motu Cordis. f Traite de la Structure du Coeur, livre i. p. 76.

\ Wagner's Handworterbuch, art. " Herzthajtigkeit."

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 789

slight admixture of true muscular fibres.* As the tendinous expansions of the
half of the segment described, bifurcate or split up, and run into similar expan-
sions from the other or remaining half of the same segment, to become strongly
embraced in the mesial line ; a complete segment may be described as consisting
of a reduplication of the endocardium or lining membrane, enclosing in its fold
certain muscular fibres, and eighteen or more tendinous expansions ; the chorda)
tendineae, on which these expansions are situated, proceeding from the anterior and
posterior musculi papillares equally (Plate XXVIII. fig. 28 a c), and pursuing diffe-
rent directions, to meet in the mesial line and form angles (Plate XXVIII. fig. 32)
which become more and more obtuse in a direction from above downwards. When,
therefore, a segment is examined by being held against the light, or by the aid
of a dissecting lens or microscope, it is found to consist of tendinous striae run-
ning transversely, obliquely, and more or less vertically ; the striae of opposite
sides being so disposed that they mutually act upon and support each other ; an
arrangement productive of great strength, and one which secures that the seg-
ments shall be at once tightened or loosened, by the slightest contraction or
relaxation of the musculi papillares. The intermediate accessory segments of
the mitral valve, resemble the principal ones, in structure and general configura-
tion. They are, however, comparatively speaking, very thin; and the chordae
tendinese inserted into them differ from those inserted into the principal seg-
ments, in having a more vertical direction, and in being longer and more feeble.
The description given of the bicuspid valve, applies, with trifling alterations in
particular instances, to the tricuspid, if allowance be made for an additional large
segment, and three or more accessory segments. With regard to the smallest of
the three large segments forming the tricuspid, I have to observe, that in all pro-
bability, it is simply an over-developed accessory segment ; the so-called tricuspid
valve being in reality a bicuspid one (Plate XXVIII. fig. 34 run). Nor is this to
be wondered at, when it is stated f that the right ventricle, is a segmented portion
of the left, and partakes of its bilateral symmetry even in matters of detail. The
opinion here advanced is by no means new, but it appears to me that the point has
not been sufficiently investigated, and we are in want of statistics regarding it.
In ten human hearts which I examined for this purpose, no less than four
had well-marked bicuspid valves in both ventricles; and on looking over a
large collection of miscellaneous hearts in the Museum of the Royal College
of Surgeons of England, I found that nearly a third of them had the pecu-
liarity adverted to ; if indeed that can be called peculiar which seems to me
to be typical. When two principal segments, with two or more accessory
segments, occlude the right auriculo- ventricular orifice, as happens in Plate

* According to Mr Savory's observations, the muscular fibre is found more particularly at the
upper or attached border of the valves.

f Phil. Trans., vol. cliv., pp. 464-67.

VOL. XXIII. PART III. 10 B

790 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

XXVIII. fig. 34 mn, the distribution of the chordae tendinese (op) in the
segments is the same as that given when describing the bicuspid of the left
ventricle ; but when there are three principal segments, with as many or
more accessory segments, the distribution is varied to meet the exigencies of
the case ; there being a tendency in each of the chordae tendinese to divide into
three ; one of the chords so divided being inserted by one of its slips into the
mesial line of the segment at the base posteriorly ; by another into the margin
of the segment, likewise at the base ; and by the remaining slip into a point
intermediate between the mesial line- and the margin. Other chords, similarly
divided, are inserted at intervals in a direction from above downwards, or from base
to apex (Plate XXVIII. fig. 34 o), the insertions in each case proceeding from the
mesial line towards the margin. In some instances, though more rarely, a mixed
arrangement prevails ; the insertions of the three tendinous slips running from
the mesial line of the segment towards the margin, and from the base to the
apex indiscriminately ; but whatever the arrangement on the one side of a seg-
ment, it is, as a rule, the same on the other, so that one of the segments of a true
tricuspid valve is as symmetrical in its way as a segment of a bicuspid one. The
musculi papillares in the right ventricle of a typical heart, are two in number, as
in the left. When, therefore, the right auriculo-ventricular opening is closed by
a tricuspid valve, an additional origin is required for the chordse tendinese ; and
in such a case these chords spring from the two musculi papillares, and from the
right side of the septum behind the fleshy pons, either from a rudimentary
papillary muscle, or from carnese columnse, or from the smooth wall of the sep-
tum. The number of papillary muscles in the right ventricle (and the same
remark applies to the left, although not to the same extent) vary somewhat ; the
two typical ones being frequently seen to bifurcate at their free extremities,
and others to spring up in their vicinity. On these occasions the origins of the
chordae tendinese are increased, but this does not materially affect their insertion,
which is remarkably uniform. The tricuspid valve, differs from the bicuspid as
regards actual strength, the segments being comparatively thinner. This deli-
cacy of structure, extends to the chordse tendinese and to the musculi papillares,
in fact, to everything pertaining to the right ventricle ; the walls of which, as is
well known, are only half the thickness of those of the left ventricle. The com-
parative feebleness of the tricuspid valve, is no doubt traceable to the smaller
amount of force it is called upon to withstand, the pulmonic circulation being
less vigorous than the systemic. From the foregoing description, it will be seen,
that the chordse tendinese are inserted into every portion of the bicuspid (Plate
XXVIII. figs. 31, 32, and 33) and tricuspid valves; and as they freely decussate
with each other in all directions, by means of their terminal brush-shaped expan-
sions, and are of infinite variety as regards length and strength ; those at the base
and posterior aspect of each segment being long and exceeding strong ; while those

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA.

791

at the margins and towards the apices are short, and in some instances as delicate
as hairs, it follows that every part of the valves in question, bears a graduated
relation to, and is under the control and domination of,- the conical-shaped spiral
musculi papillares, whose power to contract is now well established.* It is
therefore my impression, and my belief is shared by others, that the chordae ten-
dinese ought to be regarded as the satellites of the actively contracting musculi
papillares, under whose guidance they have to perform, not only a very important
but a very delicate function, and one which could not by any possibility, be
accomplished by a simply mechanical arrangement.

The Mitral and Tricuspid Valves of the Mammal in A ction.

The theories which have long divided the attention of physiologists with
regard to the action of the mitral and tricuspid valves, are two in number ; one
sect maintaining, that the valves are acted upon mechanically by the blood, as if
they were composed of inanimate matter ; the other believing, that they form
part of a living system, their movements being traceable to their connection
with the musculi papillares, which are actively contracting structures.

In the mechanical theory, the segments of the valves are supposed to be pas-
sively floated up by the blood, which acts upon them from beneath during the
systole, and brings their edges or free margins into such accurate apposition as
enables the segments completely to occlude the auriculo-ventricular orifices. In
these movements the musculi papillares and carneoe columnw are said to take no
part ; the chorda? tendinese acting mechanically, like so many stays, to prevent
eversion of the segments in the direction of the auricles.

In the vital theory, on the other hand, the segments of the valves are sup-
posed to be from the first under the control of the musculi papillares ; these
structures, by contracting, drawing the lips or free margins of the segments closely
together in the axis of the auriculo-ventricular openings, to form two impervious
cones, the apices of which project downwards into the cavities of the ventricles.

In these movements, it is maintained, the blood takes no part, the chorda? ten-
dinese, which are regarded as the proper tendons of the musculi papillares, acting
as adjusters or adapters of the segments ;j a function which their varying length
and strength readily enables them to perform.

I need scarcely add, that these theories are diametrically opposed to each

* Dr John Reid states from experiment, that the carneae column* act simultaneously with the
other muscular fibres of the heart, and that the musculi papillares are proportionally more shortened
during their contraction than the heart itself taken as a whole. He attributes this to the more
vertical direction of the musculi papillares, and to their being free towards the base and in the direc-
tion of the ventricular cavities. — Cyc. of Anat. and Fhy., art. " Heart," p. 601. London, 1839.

f In one specimen which I dissected, the chordae tendinese contained a large amount of muscular
fibre, and were so thickened as to resemble rudimentary musculi papillares.

792 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

other. The vital theory which was espoused by Mayo and Bouillaud,* has been
defended with great ability by Dr John REiD,f who says, that if the lips of the
valves were merely floated up to the orifice, a greater quantity of the blood
would regurgitate into the auricles during the systole of the ventricle than if
the lips were assisted or brought together by an active force. This author
alludes to, and very properly attaches considerable importance to the fact, that
the musculi papillares to which the valves are attached by the chordae tendinese,
contract with the other portions of the ventricular walls. He also points out the
uniform position and course of the musculi papillares and chordae tendinese, and
shows, as bearing directly upon the question, how the chordae tendinese in the
left ventricle pass from each musculus papillaris to both lips of the mitral valve.
One statement, however, made by him requires to be noticed. When speaking
of the mitral valve he says, that the lip of the posterior or smaller segment
though it may be drawn inwards so as to meet that of the larger and more move-
able one, is so bound down as to be scarcely capable, in most cases, of being floated
up on a level with the orifice. I have examined a large number of hearts, young
and old, human and otherwise, with a view to determine this point, and in no
instance do I remember an example where the peculiarity adverted to was
observable. The anterior or larger segment, from its attachments and shape,
naturally rises higher, just as the anterior and septal segments of the tricuspid
valve for similar reasons, rise higher than the posterior segment ; but in every
case, the posterior or smaller segment rises sufficiently high, not only fairly to
meet the anterior and larger one, but if a sufficiency of pressure is exercised,
to protrude in an upward direction, so as to form a convexity which encroaches
upon the left auricular space.

In the valvular controversy, as in most others, a certain amount of truth is
to be found on either side ; and I have to express my conviction, that both
theories (conflicting though they appear) are virtually correct as far as they go,
but that neither the one nor the other is sufficient of itself to explain the gradual,
and to a certain extent self-regulating process, by which the auriculo- ventricular
valves are closed and kept closed. On the contrary, I believe that the closure is
effected partly by mechanical and partly by vital means. In other words, that
the blood towards the end of the diastole and the beginning of the systole forces
the segments in an upward direction, and causes their margins and apices to be
so accurately applied to each other as to prevent even the slightest regurgita-
tion; whereas, during the systole, and towards the termination of that act,
the valves are by the contraction of the musculi papillares, dragged down by

* These investigators proposed to call the musculi papillares the tensor, elevator, or adductor
muscles of the valves,
f Op. cit. pp. 361, 362.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA.

793

the chordae tendineee into the ventricular cavities to form two dependent cones ;
this downward movement of the segments permitting the blood in the auricles to
descend into the ventricles, so as to relieve the congestion of the former.

Granting that the foregoing hypothesis is correct, there is yet another point
as to the manner of the closure, to which I am particularly anxious to direct at-
tention, as it is of primary importance, and appears to me, by some unaccountable
means, to have hitherto escaped observation. I refer to the spiral form assumed
by the blood in the ventricular cavities, which,' as has been already partially ex-
plained, causes it, towards the end of the diastole and the beginning of the systole,
to act in spiral waves mechanically (Plate XXIX. fig. 49 j q) on the segments, with
the effect of twisting and wedging them into each other in a spiral upward direction
(Plate XXIX. fig 51 m n, and figs. 53 and 54 m i n, r s). I allude, also, to the spiral
course pursued by the musculi papillares (Plate XXIX. figs. 49 and 50 xy) ; these
structures, as the systole advances, contracting in such a manner as occasions the
spiral descent of the segments into the ventricular cavities (Plate XXIX. figs. 52
and 55 m n, r s), to form two spiral dependent cones, the apices of which are directed
towards the apices of the ventricles. As the decrease of the blood in the ventricles
is followed, as has been stated, by a corresponding increase in the auricles ; the
blood in the latter assists in keeping the free margins and apices of the segments
from being everted by the uniform pressure exercised on them by the blood in
the former, during the systole. From this account of the closure of the auriculo-
ventricular valves, it will be perceived that the valvular segments form two
moveable partitions or septa, which rise and fall during the action of the heart,
in the same wTay that the diaphragm rises and falls during the respiratory efforts.
The advantages arising from such an arrangement are very great. When the ven-
tricles are full of blood, and the auricles empty or comparatively so, the valvular septa
are convex towards the base of the heart, and protrude into the auricular cavities.
When, however, the auricles are fidl of blood, and the ventricles all but drained of
it, the valvular septa descend so as to protrude in a downward or opposite direc-
tion. Certain portions, therefore, of the auriculo-ventricular cavities are common
alike to the auricles and to the ventricles ; and it is important to note this fact, as
the valvular septa by their rising and falling, at one time increase the size of the
ventricular cavities while they diminish the auricular ones, and vice versa. The
principal object gained by the descent of the segments into the ventricles is
the diminution of the ventricular cavities towards the base ; the dependent cones
formed by the valves fitting accurately into the conical-shaped interspaces situated
between the slanting heads of the musculi papillares and the auriculo-ven-
tricular tendinous rings. As the musculi papillares, on the contraction of the
ventricles, mutually embrace and twine round each other, the obliteration of
the ventricular cavities is by this arrangement rendered very complete. " That
the ventricles empty themselves during the systole, is rendered probable
VOL. xxiii. part in. 10 c

794 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

from analogy, for on watching the hearts of cold-blooded animals, they are
found towards the end of the contractile act to become quite pale, not, as Harvey
supposed, from the blood being pressed out of the parietes, but from the blood
in their cavities seen through their transparent sides being almost entirely
expelled." An important inference to be deduced from the spiral nature of
the ventricular fibres and ventricular cavities and the undoubted spiral action
of the auriculo-ventricular valves is the effect produced on the blood as it leaves
the ventricles, that fluid being unquestionably projected by a wringing or twist-
ing movement, which communicates to it a gliding spiral motion. This view is
favoured by the spiral inclination of the sinuses of Valsalva to each other, these
structures gradually introducing the blood so projected into the vessels. How far
the rotatory movement referred to, extends into the arteries, is difficult to deter-
mine; but when the smooth cylindrical nature of the vessels, and the great
velocity and force with which the blood travels, is taken into account, there is
every reason to suppose that the distance is considerable.

The Mechanical and Vital Tlieories of the Action of the Mitral and Tricuspid Valves

considered.

That the theory which attributes the closure of the auriculo-ventricular
valves to the mechanical floating up of the segments from beneath by the blood,
forced by the auricles* into the ventricles, distending equally in all directions,!
is of itself inadequate to explain all the phenomena, is, I think, probable from
analogy and the nature of things ; for if a merely mechanical arrangement of parts
was sufficient for the closure of the gradually contracting auriculo-ventricular
orifices, then, it may be asked, why were these apertures in birds and mammals
not furnished with sigmoid or semilunar valves similar in all respects to those
met with in the veins and arteries ? The answer to this question is no doubt to
be found in the nature of the structures in which the valves are situated, as well
as in the circulation itself. In the veins, as is well known, the movements of the
blood are sluggish — the contraction of the vessels being feeble, and not conse-
quently calculated to interfere to any great extent with the closure of the valves.
In the arteries, where the circulation is more vigorous, and the contractions of the
vessels more decided, the valves are surrounded by dense fibrous rings, which
protect them alike from the contractions of the ventricles, and the contractility

* According to Harvey, Lower, Senac, Haller, and others, the auricles contract with a very
considerable degree of energy.

f "In a quantity of fluid submitted to compression, the whole mass is equally affected and
similarly in all directions." — Hydrostatic Law. Dr George Britton Halford attributes the
closure of the auriculo-ventricular valves entirely to the pressure exercised by the auricles on the
blood forced by them into the ventricles. That, however, this is not the sole cause, will be shown
further on.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 795

and elasticity of the vessels. In the bulbus arteriosus of fishes, where the area
of activity of the valves is not thus circumscribed, and where they are exposed
to the influence of muscular contraction, the segments are not only increased
in number, but chorda? tendinea?, in the shape of tendinous bands, begin to make
their appearance. In the auriculo-ventricular valves of fishes and reptiles,
chorda? tendinece in various stages of development occur, these being attached to
the interior of the ventricle to more or less fully developed musculi papillares ;
the musculi papillares, which occur only in the reptilia, being in no instance
so well marked as in the ventricles of the aves and in the mammalia. As we
thus rise in the scale of being, and the requirements of the circulation become
greater, it will be observed that the relation of the segments to actively contracting
structures, becomes more and more defined. In the ventricle of the fish, as I
pointed out, the fibres proceed in wavy lines from base to apex, and from apex
to base, from without inwards and circularly ; so that the organ contracts and
dilates very much as one would shut and open the hand. In the reptilia, the
external and internal fibres pursue a slightly spiral direction— the ventricles
rotating more or less when in action. In the cold-blooded animals, moreover, as
every one is aware, the circulation is languid or slow, so that an arrangement
of valves similar in some respects, though more complex than that which exists
in the veins and venous sinuses and in the arteries, amply suffices. In the hearts,
however, of the warm-blooded animals, where the ventricles are composed entirely
of spiral fibres, and where the circulation, on account of the sudden twisting
and untwisting of the fibres is very rapid, a system of valves, which will act with
greater rapidity and precision, is absolutely necessary. But functional precision
implies structural excellence ; and hence that exquisite arrangement of parts in
the auriculo-ventricular valves of mammals,, whereby every portion of every
segment (by reason of the ever varying length and strength of the chordae
tendinese) bears a graduated relation to the musculi papillares and carneae
cohmmce. Although the partial closing of the valves during the diastole may be,
and is occasioned by the uniform expansion of the blood owing to the force
exercised upon it by the contraction of the auricles, still it must be evident to all
who reflect, that this cause is not of itself adequate to the complete closure, and
for a very obvious reason. The blood, which is the expanding force, derives its
power solely from the contraction of the auricles, and enters the ventricular
cavities by the auriculo-ventricular orifices. Once in the ventricles, however,
the blood has no inherent expansive power, by which it can of its own accord
entirely shut off or close, the apertures by which it entered. This act, as I shall
show presently, requires for its consummation, the force exercised by the con-
traction of the ventricles at the commencement of the systole. Admitting, how-
ever, that the expansion of the blood was adequate to the closure of the auriculo-
ventricular valves at one period,— say at the end of the ventricular diastole,

796 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

when the ventricles are full of blood and the auriculo-ventricular orifices widest, —
it is scarcely possible that it could keep them closed towards the end of the
systole, when the auriculo-ventricular orifices are greatly diminished in size and the
blood itself all but ejected. A regulating and motor power, therefore, in addition
to the blood, for adapting the different portions of the segments of the valves to
the varying conditions of the auriculo-ventricular orifices and cavities during
the systole, seems requisite. Such a power, in my opinion, resides in the conical-
shaped spiral musculi papillares with their proper tendons— the chordae tendinese.

That the theory which ascribes the closing of the auriculo-ventricular valves,
entirely " to the contraction of the musculi papillares," is likewise of itself in-
sufficient, appears for the following reasons : —

1st, If the valves which, at the commencement of the ventricular diastole, hang
free in the ventricular cavities, and are undoubtedly floated mechanically upwards,
so as to have their edges approximated by the blood towards the termination of
that act, were dragged upon at the instant of contraction from above downwards,
or in an opposite direction to that in which the force by which they were brought
together acts, the segments of the valves, instead of being further approxi-
mated, would inevitably be drawn asunder, and regurgitation to a fatal extent
supervene.

2d, By such an arrangement as Dr Halford has satisfactorily shown, the
cavities of the ventricles would not only be materially diminished at a very in-
convenient time,* but a certain amount of the force required for the expulsion of
the blood from the ventricular cavities, would be expended in closing the valves.
While, therefore, it seems essential for the apj roximation of the auriculo-ventri-
cular valves, that they should first ascend with the ascending columns of blood
occasioned by the injection of the ventricles by the auricles, so as to have their
margins gradually and accurately approximated, in order that when the contrac-
tion of the ventricles takes place, they may be instantly closed,f thereby effect-
ually preventing regurgitation ; so, for their continued closure, it seems necessary,

* Dr Halford states his belief, " that the segments of the valves are forced even beyond the
level of the auriculo-ventricular orifices, and in this way become convex towards the auricles, and
deeply concave towards the ventricles." In his zeal for the enlarged accommodation of the ventricles,
he forgets that the auricles are equally entitled to consideration, and that it is unfair to give to the
one and take from the other ; for if, as he argues, the segments of the valves form a convex partition,
whose convexity throughout the entire systole of the ventricle points in the direction of the auricles,
the space beyond the level of the orifices is appropriated from the auricles without compensation. As,
however, such an arrangement could not fail materially to inconvenience the auricles, when they
are fullest of blood, we naturally turn to the ventricles for redress. The additional space required
is, as I have already shown, supplied by the descent of the segments of the bicuspid and tricuspid
valves towards the end of the systole when the ventricles are almost drained of blood. — On the
Time and Manner of Closure of the Auriculo-ventricular Valves. Churchill, London, 1861.

f The margins of the segments of the valves at the end of the ventricular diastole are so close
as to be nearly in contact. The slightest amount of pressure, therefore, suffices for the instantaneous
closure. As, moreover, regurgitation is prevented in proportion to the rapidity with which the
closure is effected, the efficiency of this arrangement is at once apparent.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA.

797

in the second place, that they should descend with the rapidly decreasing columns
of blood occasioned by the uniform and continued contraction of the ventricles
and musculi papillares, in order that they may adapt themselves to the reduced
size of the auriculo-ventricular orifices, and in order that the ventricular cavities
ma}' be diminished towards the base, as well as in every other direction. My belief
consequently is, that the valves, like the ventricles themselves, have a passive and
an active state ; and another which, while it is neither strictly passive nor active,
may, for the sake of distinction, be regarded as the neutral state. The passive
state, corresponds to the diastole of the ventricles ; the active state, to the systole ;
and the neutral or intermediate state, to that brief period which embraces the
termination of the diastole and the commencement of the systole.* As, however,
the action of the valves, is, to a certain extent, dependent upon, and induced by
the action of the ventricles, the following slight differences as regards time, are to
be noted. The passive state of the valves corresponds to that period in which
their segments are floated mechanically upwards, and their margins partially
approximated (Plate XXIX. figs. 52 and 55 mn, rs) by the blood forced by the
auricles into the ventricles, during the dilatation of the latter ; the neutral state, to
that almost inappreciable interval which succeeds the sudden contraction of the
ventricles, in which the blood set in motion is arranged in spiral columns, and
acts in such a way as not only instantly closes the valves (Plate XXIX. figs.
53 and 56 mn, rs), but screws and wedges the segments thereof, into each other,j- in
an upward spiral direction (Plate XXIX. figs. 54 and 57 mn, rs). The active
state, corresponds to the period occupied by the progressive contraction of the
ventricles. During this period, the valves are dragged forcibly downwards by the
contraction of the musculi papillares, in an opposite direction to that by which they
ascended ; and are twisted into or round each other, to form spiral dependent cones.
In the active stage, as in the neutral, the blood acts from beneath, and keeps the
delicate margins and apices of the segments of the valves, in accurate contact.
That the foregoing is the true explanation of the gradual approximation and con-
tinued closure of the auriculo-ventricular valves, there can, I think, be little doubt,
both from the disposition and structure of the parts, and from experiment. If,
e.g., the coagula be carefully removed from perfectly fresh ventricles, and two
tubes of appropriate calibre be cautiously introduced past the semilunar valves,
and securely fixed in the aorta and pulmonary artery, % and the preparation be

* In speaking of the closure of the valves, it is of great importance to remember, that the action,
although very rapid, is a strictly progressive one, and necessarily consists of stages. In this, how-
ever, as in many other vital acts, it is often very difficult (if not indeed impossible) to say precisely
where the one stage terminates and the other begins.

f This act takes place just before the blood finds its way into the aorta and pulmonary artery,
the amount of pressure required for shutting and screwing home the auriculo-ventricular valves being
less than that required for raising the semilunar ones.

\ Strictly speaking, the tubes should be introduced into the auriculo-ventricular orifices, as it
is through these apertures that the blood passes during the dilatation of the ventricles. As, however ;

VOL. XXIII. PART III. 10 D

I

798 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

sunk in water until the ventricular cavities fill, it will be found, when one of the
tubes,* say that fixed in the aorta, is carefully blown into, that the segments of
the bicuspid valve roll up from beneath in a spiral direction (Plate XXIX. figs.
52 and 55 rs), in a progressive and gradual manner ; each of the two larger or
major segments, by folding upon itself, more or less completely, in a direction from
within outwards, forming itself into a provisional or temporary cone, the apex of
which is directed towards the apex of the left ventricle {first stage, in which the
crescentic margins and apices of the segments are slotvly approximated by the uniform
expansion of the blood forced into the ventricle by the auricle). As the pressure
exerted by the air is gradually increased, and the action of the valve is further
evolved, the segments, folded upon themselves as described, are gradually elevated,
until they are on the same plane with the auriculo -ventricular fibrous ring; where
they are found to be wedged and screwed into each other, and present a level
surface above (Plate XXIX. figs. 53 and 56 rs).

At this, the second stage of the closure, the crescentic margins of the segments
are observed to be accurately applied to each other, to form two perpendicular
crescentic walls, which accord in a wonderful manner with similar walls formed
by the union of the semilunar valves ; in fact, the manner of closure is, to a
certain extent, the same in both ; the segments in either case, being folded upon
themselves by the blood, and presenting delicate crescentic margins, which are
flattened against each other, in proportion to the amount of pressure employed.
When the crescentic margins of the segments, are so accurately applied to each
other as to become perfectly unyielding, and the distending process is carried
beyond a certain point, the bodies or central portions of the segments bulge in an
upward or downward direction as happens ; the segments of the mitral valve,
protruding into the auricle (Plate XXIX. figs. 54 and 57 rs) ; those of the semi-
lunar one, into the ventricle (Plate XXVIII. figs. 27 and 28 v wx).

This completes the first and second stages of the process, by which the mitral
or bicuspid valve is closed ; but the more important, as being the more active
and difficult, is yet to come. This consists in adapting the segments of the valve, to
the gradually diminishing auriculo- ventricular orifice ; and in dragging them down into
the left ventricular cavity, to diminish the ventricle towards the base. By this
act, the segments, as has been shown, are made to form a spiral dependent cone,
an arrangement which renders the obliteration of the ventricular cavity towards
the base, a matter of certainty.

The third stage of the closure of the mitral valve, entirely differs from the

the insertion of tubes, however small, into the auriculo-ventricular openings would necessarily prevent
the complete closure of the valves, there is no good reason why the plan recommended in the text
should not be adopted.

* Thin metallic tubes with unyielding parietes are best adapted for this purpose, as they can
be readily fixed in the vessels, and the amount of pressure exercised by the breath on the valves
asily ascertained.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA. 799

first and second stages ; inasmuch as the chordae tendinese, on the contraction of
the musculi papillares, drag the segments in a downward direction, to adapt them
to the altered conditions of the auriculo-ventricular orifice, and ventricular cavity.
That this downward movement, actually takes place, is proved as follows. If a
portion of the fluid be withdrawn by applying the mouth to the tube in the aorta,
so as to create a certain amount of suction, the segments of the bicuspid valve, are
found gradually to descend in a spiral direction (Plate XXIX. figs. 52 and 55 r s) ;
forming, as they do so, a spiral cone, whose apex becomes more and more defined
in proportion as the suction is increased ; the water in the interior keeping the
margins of the segments, accurately in apposition, and thereby maintaining the
symmetry. If, again, the musculi papillares, be cut out of the ventricular walls
and made to act in the direction of their fibres, i. e., in a spiral direction from left
to right downwards ; they will be found, in virtue of being connected by the
chordse tendinese more or less diagonally to either segment of the bicuspid valve,
to act simultaneously on that side of the segment which is next to them ; the
musculus papillaris marked a b in fig. 31, Plate XXVIII., acting spirally on the
margin and apex (oc) of the larger or anterior segment, in the direction of the
arrow near it; that marked cd, acting spirally on the margin and apex (v) of the
smaller or posterior segment, in a precisely opposite direction. (Compare direc-
tion of arrows marked a and d.) The effect of these apparently incongruous
movements, on the segments, is very striking.

The space which naturally exists between the segments (Plate XXVIII. fig.
31 v x\ fig. 28 m n), and which corresponds to the distance between the points
of origin of the two sets of chordse tendinese [a and J), is gradually but surely
diminished, and the segments twisted into or round each other.

This arrangement, I may observe, while it facilitates the spiral movement
adverted to, absolutely forbids any other.

It is rendered perfect by the pressure exercised on the delicate margins of
the segments by the spiral columns of blood as already explained.

One complete closure of the mitral or bicuspid valve, may therefore be briefly
stated, as follows : —

The segments, are first floated gently and gradually upwards, by the uniform
expansion of the blood forced into the left ventricle, during the diastole, by the
contraction of the left auricle. This is a purely mechanical act, and during its
performance the valve, and chordce tendinece, are entirely passive. When, however,
the ventricle suddenly contracts, the margins of the valve, which were in
apposition, although not in actual contact, are rapidly approximated (the left
auriculo-ventricular opening being instantly closed*) ; and the two spiral columns

* Regurgitation (as has been already stated) is prevented in the inverse of the rapidity with
which the closure takes place.

800 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

of blood set suddenly in motion by the ventricular systole, force the segments of
the valve, in an upward spiral direction, rendering them more and more tense
until they reach the level of the ventricular orifice ; at which point, they are twisted
and wedged into each other ; the chordae tendineae limiting the amount of upward
motion, to prevent retroversion and regurgitation. As, however, the blood
finds its way through the aorta, which it does the instant the segments of the
valve are screwed home,* the segments gradually hut rapidly descend in an opposite
direction to that hy luhich they ascended, their descent heing occasioned, regulated, and
minutely graduated hy the contraction of the musculi papillares aided hy the chorda?
tendineos and hy the ascending spiral columns of hlood ; an arrangement which insures
that the delicate margins of the segments, are always closely and accurately
applied to each other ; for the chordae tendineae and the blood in the auricles act-
ing from above, while the spiral columns of blood in the ventricles act from beneath,
the delicate margins in question, are effectually prevented from falling towards
the ventricular walls.f This downward action of the valve, musculi papillares,
and chordae tendineae, which is of essential importance in adapting the former to
the diminishing condition of the left auriculo-ventricular orifice and ventricular
cavity, continues until the blood is completely ejected, and the segments of the
valve are twisted or plaited into each other to form a dependent spiral cone,
whose apex, is directed towards the apex, of the ventricle. • By the time this
happens, i. e., by the time the blood is ejected from the ventricle, and the cone in
question fairly formed, the left auricle is distended ; and due advantage being
taken of the extra space afforded by the descent of the valve, the blood assumes
a spiral and conical or wedge-shaped form, which is the best possible for pushing
aside the segments, already in the most favourable position for falling away from
the ventricular axis, towards the ventricular walls. The same phenomena are
repeated with unerring regularity, with each succeeding action of the heart.
What has been said of the manner of closure of the mitral or bicuspid valve,
applies, I need scarcely add, with slight modifications to the tricuspid.

Eesume.

The points which have been more particularly dwelt upon in the present
investigation, and on which the writer has endeavoured to throw additional light,
are these : —

* Wlien the segments of the mitral valve are screwed home, the whole force of the ventricular
contraction is expended in raising the aortic semilunar valve, and until the screwing home has taken
place, the latter action is impossible, as the ventricle up till this point is compressible.

t The serious results which might arise from the segments of the valve falling towards the
ventricular walls, or away from the axis of the cavity, is especially prevented by the attachments of
the chordae tendinese ; the principal and more internal chordae tendinese (Plate XXVIII. fig. 33 r s)
being, as I have shown, attached to the backs or more external surfaces of tbe segments, an arrange-
ment which makes their rapid approximation towards the ventricular axis inevitable.

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBTIATA. 801

First, An attempt has been made to point out the intimate structural rela-
tion, existing between the veins, and venous valves ; how the segments of the
venous valves are composed principally of white fibrous and yellow elastic tissue^
arranged in at least three well-marked directions ; and how the segments are so
disposed, that their free margins, unless when the blood is actually passing
between them, are always more or less in apposition. An attempt has also been
made, to demonstrate the nature of the apposition, by the employment of plaster
of Paris, injected while in the fluid state into the distal and proximal extremities
of the vessels. In the veins, as was pointed out, the closiwe is to a great extent
mechanical ; the segments, when two are present, being forced together in the
mesial plane of the vessel, by the contraction of its walls, but principally by the
weight of the refluent blood.

Secondly, The structure and relations of the arterial or semilunar valves,
particularly in man, have been examined afresh ; a more precise description than
that hitherto given of the segments in systematic treatises on anatomy having
been essayed. The great vessels have further been shown to bifurcate at their
origins, and to be greatly thickened between the segments, which they support
and incline towards each other — an arrangement calculated to bring the free
margins of the segments more or less closely together, unless when pushed
aside by the advancing column of blood during the systole. The sinuses of
Valsalva have, in addition, been shown to vary in size ; the one curving towards
the other in a spiral direction, and causing the blood to act in spiral waves
upon the segments of the semilunar valves, which by this means are twisted and
wedged into each other, when the reflux occurs. In the arteries, the action of the
semilunar valves, as has been explained, is for the most part mechanical, the strong
fibrous rings situated at the aortic and pulmonic orifices, tending to counteract
the inconvenience, which might be supposed to result from an excess of vital
contractility in the vessels, and the ventricles. The arterial semilunar valves,
may be said to differ from the bi-semilunar venous ones, in having their segments
wedged together by a spiral movement, which in the venous valves, is little more
than indicated.

Thirdly, The bulbus arteriosus of fishes, has been shown to be a contractile
organ, and to contain in its interior a system of valves, the segments of which, are,
as a rule, more numerous than in either the veins or arteries. They have, in
some instances, tendinous bands, resembling chordae tendinese, running between
them ; and are for the most part, arranged in tiers ; so that the blood which is
not caught by the one set, falls into, and is supported by the next. The action of
these valves, as will readily be inferred, is partly mechanical, and partly vital; for
the contraction of the bulb must be regarded as contributing to the closure.
They are, therefore, an advance upon the valves of the veins and arteries, both
as regards their number, and the manner of their closure.

VOL. XXIII. PART III. 10 E

802 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

Fourthly, In the reptiles, as has been demonstrated, the valves are partly
tendinous, and partly muscular ; while in the right ventricle of the bird, they are
altogether muscular. Here, then, may be witnessed the first trace of a self-
regulating power — actively contracting muscular fibre, taking the place of non-
contractile fibrous tissue.

In the auriculo-ventricular valves, there is immense variety ; these including
most of the forms referred to, and others exhibiting a still higher degree of differ-
entiation. They are, for the most part, characterised by the presence of chordae
tendinese, which connect them with the interior of the ventricles, or the structures
arising therefrom ; viz. the earner eolumnse and musculi papillares. The auriculo-
ventricular valves, therefore, differ from the semilunar valves proper. In some
instances, only one semilunar flap is present ; and this may be either altogether
fibrous, or partly fibrous and partly muscular, or altogether muscular. In a
second, there are two flaps or segments, so arranged that their long diameters
correspond to the direction of the muscular fibres lining the ventricular cavity ; the
segments being continuous with the muscular fibres referred to. In a third, the two
segments are attached to the interior of the ventricle by rudimentary chorda? ten-
dinew. In a fourth, two accessory or smaller segments, are added to the two
principal ones ; the whole being attached by well developed chordae tendinece to rudi-
mentary musculi papillares. In a fifth, which is the most perfect form of valve,
as it exists in man and in the higher mammalia, the segments are from four to
six in number, most exquisitely and symmetrically formed, and attached by minutely
graduated chordce tendinece to highly developed cameo? columnar and spiral mus-
culi papillares.

The action of the auriculo-ventricular valves, owing to the want of uniformity
in the number, structure, and relations of their segments, is varied. It is, how-
ever, on all occasions, carefully adapted to the wants of the circulation, and to
the configuration of the ventricles and ventricular cavities ; these cavities, as
has been pointed out, adapting or moulding the blood, and causing it to act in
given directions. Thus in the fish, where the circulation is slow, and where the
ventricle is conical in shape, and composed of fibres interlacing in all directions,
the segments, where two are present, are forced towards each other by the uniform
expansion of the blood, and by the contraction of the ventricles, in a manner
analogous to that by which the segments of the bi-semilunar venous valves are
approximated by the retrogressive movements of the slowly advancing venous
blood, assisted to a slight extent by the vital contractility of the vessels.

In the reptile, where the circulation is also languid or slow, the shape of the
ventricle, owing to the fibres pursuing a more or less spiral direction, is that
of a cone slightly twisted upon itself. As the spiral arrangement extends
also to the valves, their action may be aptly compared to that which obtains
in the valves of the largest veins, and in the arteries. It is, however, in the

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA.

803

auriculo-ventricular valves of the bird and mammal, that the spiral action of
the segments becomes most conspicuous ; the nature of the action being unavoid-
ably determined, by the unmistakably spiral arrangement of the muscular fibres
composing the ventricles, and by the spiral nature of the musculi papillares and
ventricular cavities. As, however, the action of these valves, has been already
explained at great length, further allusion to them at this stage is unnecessary.

The valves of the vascular system of the vertebrata, as will be perceived
from this summing up, form a progressive and gradually ascending series ; the
valves in the veins exhibiting a lower type than those in the arteries ; the valves
in the arteries, being less fully developed than the valves occurring in the
bulbus arteriosus and in the auriculo-ventricular orifice of the fish ; the valves
in the fish, being less highly differentiated than the valves in the reptile and
bird ; these again falling short both in complexity and adaptive power to those
met with in the mammal. In the mammal the valvular arrangements may be
said to culminate.

i Description of the Plates.

Plate XXVIII.

Figs. 1 and 2. External Jugular Veins of Horse inverted. Show valves, consisting of two (d e),
three (a b c), and four (/ g h) segments. (See pp. 763, 764.)

Fig. 3. Section of External Jugular Vein of Horse. Shows valve, consisting of two segments (ab),
with dilatations (g), corresponding to the sinuses of Valsalva, in the arteries. (See pp. 763,
764, 767.)

Fig. 4. External Jugular Vein of Horse opened. To show the relations of the segments (a b)
above (r e). (See p. 763.)

Fig. 5, Portion of Femoral Vein distended with plaster of Paris. Shows dilatations (h g) in the
course of the vessel corresponding to the position of the valve. (See p. 765.)

Fig. 6. Shows Venous Valve, consisting of two segments (ab), in action. (See p. 767.)

Fig. 7. The same, not in action. (See p. 763.)

Fig. 8. Venous Valve from External Jugular of Horse, consisting of three segments. (See p. 764.)

Fig. 9. Venous Valve, consisting of one segment, situated at the entrance of a smaller into a larger
vein. (See p. 763.)

Fig. 10. Venous Sinus from Auricle of Heart of Sturgeon. (See p. 782.)

Fig. 11. Femoral Vein distended with plaster of Paris. Shows venous valves in action, where a
smaller vessel enters the larger one (a b), and in the main trunk (a' b'). (See pp. 767, 768.)

Fig. 12. Vertical Section of Vein distended with plaster of Paris. Shows the nature of the union
between the segments (e). (See p. 767.)

Fig. 13. The same, the section being carried between (e) instead of across or through the segments.
(See p. 767.)

Figs. 14, 15, and 16. Show the Structure of the Venous Valves. (See p. 766.)

Fig. 17. Section carried thiough Pulmonary Artery and Right Ventricle of Human Heart, between
the segments of the semilunar valves (s). Shows the variation in the thickness of the
vessel (a b), and how it bifurcates (r r') at its origin. (See p. 770.)

Fig. 18. A similar section, carried through the middle of one of the segments (s). Shows how the
Pulmonary Artery (a b) behind the segments diminishes in thickness in a direction from
above downwards (i). See p. 770.)

801

DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION,

Figs. 19, 20, 21, 22, 23, and 24, Show the Structure of the Semilunar Valves in the Human Pul-
monary Artery. (See pp. 772, 773, 774, 775.)

Fig. 25. Human Semilunar Valve distended with plaster of Paris, and one of the segments (g) re-
moved, to show the precise shape of the lunula?, or opposing surfaces (b £>'), between which
union takes place when the valve is in action. (See pp. 776, 777.)

Fig. 26. Shows the spiral relation of the Sinuses of Valsalva to the segments (v iv x) of the semi-
lunar valve in the Human Pulmonary Artery, and how the segments are spirally wedged
into each other, and fixed by six non-symmetrical semilunar surfaces, to form three per-
pendicular crescentic walls (rso). Seen from beneath. (See pp. 776, 777.)

Fig. 27. Shows the Semilunar Valves in the Heart of the Sheep (y w x) distended with plaster of Paris,
or as they appear in action, together with the spiral nature of that action. (See pp. 776,
777.)

Fig. 28. Shows the same in the Aorta (v w x) of the Human Heart, and in addition, the bifid nature
of the musculi papillares (a b, c d), and the distribution of the chordae tendineae to both
segments of the mitral valve (mn). (See pp. 776, 777, 787, 788, 789.)

Fig. 29. Vertical Section carried through the Aorta and through the middle of one of the segments
of the Semilunar Valve of the Whale. Shows the variation in the thickness of the vessel
(c e), and the structure of the semilunar valve (ars' 6). (See pp. 770, 773, 774.)

Fig. 30. Shows Arterial and Auriculo-ventricular Orifices, with their fibrous rings (xvnn'). (See
pp. 769, 770.)

Fig. 31. Human Mitral Valve, Chorda? tendinea?, and Musculi papillares inverted. Shows the bifid
nature of the musculi papillares (a 6), and the threefold distribution of the chorda? ten-
dinese (s). (See pp. 786, 787, 788, 788.)

Fig. 32. Shows Structure of the Mitral Valve in the Sheep. (See pp. 786, 787, 788, 789.)

Fig. 33. Anterior Segment of Human Mitral Valve. Shows the threefold distribution of the chordse
tendinea?, from above downwards, and from the mesial line towards the margin of the
segments. (See pp. 786, 787, 788, 789.)

Fig. 34. Example of Mitral Valve in the Right Ventricle of the Human Heart. (See pp. 789, 790,
791.)

Fig. 35. Vertical Section, carried through the aorta (a a') semilunar valve (s s' s"), left auricle
(cl d', y y'), the segments of the miti-al valve (in m', n n), and the left ventricle (v vf), of the
Human Heart. Shows the greater thickness of the aorta, where the segments of the semi-
lunar valve unite above (b b', c c'), and its greater tenuity behind the centre of each seg-
ment (o) ; also how a portion of the aorta (p) is continued into the larger or anterior seg-
ment of the mitral valve (m m). It also shows the relation of the left auricle (y y', dd')
to the aorta (a a'), mitral valve (m m', n n'), and left ventricle (y v').

r r', Openings of coronary arteries.

ii n', Segments of semilunar valve uniting above.

x x', e e', Auricle terminating by wedge-shaped process in mitral valve.
s z\ Left coronary artery.

1 1' t", Convex, or attached borders of segments of semilunar valve.
g, Septal wall of left ventricle.
h h'} Chordae tendinese.
i i', Musculi papillares.

w', Apex of left ventricle. (See pp. 770, 771).
Fig. 36. Left Ventricle of Human Heart laid open to show the semilunar (ss') and mitral (m) valves
in situ. (See pp. 770, 771.)

Plate XXIX.

Fig. 37. Portion of Heart of Sturgeon. Shows auriculo-ventricular valve (a) with three chorda?

tendineae (6) proceeding from it. (See p. 781.)
Fig. 38. Ventricle and Bulbus Arteriosus of Skate laid open. Shows several rows of semilunar

valves (a b c) increasing in size in a direction from below upwards. (See p. 779.)

OF THE VALVES OF THE VASCULAR SYSTEM IN VERTEBRATA.

805

Fig. 39. Bulbus Arteriosus and Ventricle of Sturgeon, — the former displaying five rows of semi-
lunar valves (a), the latter an auriculo-ventricular valve (6), with numerous tendinous
bands running into it. (See p. 779.)

Fig. 40. Bulbus Arteriosus and Portion of Ventricle of Lepidosteus. Shows the great thickness of
the bulb («), and of the valves (b) contained within it, and between which tendinous
bands run. (See p. 780.)

Fig. 41. Portion of Bulbus Arteriosus of Basking Shark. Shows the great thickness of the bulb
(a) aud of the valves (6), and how the latter support each other. (See p. 780.)

Fig. 42. Heart of Crocodile. Shows spiral semi-muscular, semi-tendinous valve (r), situated between
right auricle (a) and ventricle (x). (See p. 781.)

Fig. 43. Bulbus Arteriosus and Ventricle of Sun-fish. Shows three semilunar valves (as b c) at orifice
of bulb, and an auriculo-ventricular valve (/), consisting of two segments. (See pp. 779,
781.)

Fig. 44. Heart of Serpent (Python tigris). Shows muscular semilunar valve at orifice of left superior
cava (s) ; also spiral muscular slit (r), occurring between the ventricles. (See pp. 781, 782).

Fig. 45. Heart of Emu, showing spiral muscular valve (g h), occurring in right auriculq- ventricular
orifice. (See p. 781.)

Fig. 46. Heart of Swan, with right and left ventricles laid open. Shows spiral muscular valve of
right ventricle (i), and mitral valve (y) of left, and how one portion of the former (j)
corresponds in position to the anterior musculus papillaris (y) of the latter. (See p. 781.)

Fig. 47- Heart of Frog-fish. Shows three sets of semilunar valves ; one occurring where the large
veins join the auricle (c) ; a second, where the auricle opens into the ventricle (6) ; the
third being situated at the orifice of the bulbus arteriosus (a). (See p. 779.)

Fig. 48. Bulbus arteriosus and portion of Ventricle of Grey Shark. Shows semilunar valves, with
tendinous chords running between them (a) ; also, auriculo-ventricular valve (g). (See pp.
779, 780.)

Fig. 49. Wax cast of Left Ventricle (b) and portion of Right Ventricle (a) of Deer. Shows spiral
nature of the left ventricular cavity, — the spiral course or tracks of the musculi papillares
(x 3/), and how between these, two spiral grooves (J q) occur, which direct the blood on to
the segments of the mitral valve in spiral waves. (See pp. 784, 785.)

Fig. 50. Plaster of Paris cast of Right and Left Ventricles of Zebra. Shows infundibulum or conus
arteriosus (1) of right ventricle, and analogous portion of left ventricle (p 0) ; also three
prominences on each (d ekr v), corresponding to the sinuses of Valsalva. It also shows
the double cone formed by the left ventricular cavity, the one apex pointing towards the
apex of the heart (j), the other towards the aorta (h). (See pp. 784, 785.)

Fig. 51. Same cast seen posteriorly. Shows the mitral (m n) and tricuspid (g h) valves in action,
and how the blood, when these are closed, assumes a conical form (0) for pushing aside
the segments of the semilunar valves, and causing them to fall back upon the sinuses of
Valsalva (y w). It also shows how the right ventricular cavity (c) curves round the
left one (x), and how the pulmonary artery (6) and aorta (A) pursue different directions
(See pp. 784, 785.)

Figs. 52, 53, and 54. Show the Mitral (>• s) and Tricuspid (mi n) Valves of the Sheep in action. How
the segments, acted upon by the spiral columns of blood, roll up from beneath towards the
end of the diastole (fig. 52) ; how, at the beginning of the systole, they are wedged and
twisted into each other, on a level with the auriculo-ventricular orifices (fig. 53) ; and
how, if the pressure exerted be great, they project into the auricular cavities (fig. 54)
(See pp. 796, 797, 798, 799, 800, 801.)

Figs. 55, 56, and 57. Show the same in the Human Heart, with this difference, that in the right
ventricle, a true mitral valve (m n), as not unfrequently happens, has taken the place of
the tricuspid. (See pp. 796, 797, 798, 799, 800, 801.)

Note. — The spiral downward movement of the mitral and tricuspid valves has only been partially
represented (figs. 52 and 55) owing to the great difficulty experienced in representing spiral
cavities.

VOL. XXIII. TAUT III. 10 F